I've been thinking about this a lot lately. WotC pumping out content like it's on a conveyer belt set to "Superspeed" has meant there are so many books out now that you can literally fill a bookshelf.
This "superspeed" has been pointed out since at least the 80s. I feel it's actually slower than 3E, but that's my opinion.
I was at a gaming store just recently and noticed half a wall filled with D&D 4e and I asked the storeperson about it and he replied, "There's a few titles we don't have but we can get whatever you want in pretty quick," and I was like, "There's more?"
That has to have a nasty overhead for WotC. TSR's problems started with having too much stock. Half their funds were tied up in warehouses. And with DDI, the only reason to buy many of the books is because you like the feel of a dead-tree in your hands.
They gauge thier sales numbers for previous similar products, guestimate potential sales, and fire off a suitable print run. Printing too many is costly at the printer, and costly at the store level as stores don't want to sit on inventory (it's taxable) if it doesn't sell, and thus wotc hears about it.
If a line doesn't sell as well, they don't print as many of the next in the line or cancel the line altogether. Simple business sense, and it looks to me as if they have been following it, experimenting and seeing what works.
The argument that PDF's or other digital copy makes it easier for pirates to pirate is a fallacy. No matter what protections you have, whether you print on paper or in pure digital, you will never, ever, kill piracy. Companies may as well just view it as money they wouldn't have made, rather than money lost. People who pirate will continue to do so, and people who buy copies will continue to do so. The size of your market remains exactly the same, whether it's digital or print.
While i'm not entirely certain, i believe that if you don't make some attempt to protect your brand / product, your investors can sue you. If it were my product, i'd want to break the kneecaps, burn down the house and salt the fields of every pirate that stole my hard work, but that's just me
Wotc is proven to have a hard time with digital initiatives, so until they can come up with a solution to make pdf style profitable, yet more secure, I don't blame them for taking thier digital ball and going home when ppl urinate in thier soda.
In a previous thread I started about errata being incorporated into a POD solution, it was pretty clear that wasn't an answer. But maintaining an updated copy of PDF's online for continuous download linked to your subscription, ie. you can download an update to whatever product you own as long as you're a subscriber to DDI, seems like a viable idea.
Not when you have to devote personnel to editing and layout for a digital version. You have page numbers that will be adjusted, and you would have to track down all the references to that particular page and make sure it's updated. This is not impossible, could probably be automated somehow(not familiar with publishing and layout side of the software industry), but it takes time, money, and they have a hard enough time preventing "page xx" from making it to final product.
It becomes a balance of cost vs return on investment. If there is enough demand for that from recurring paying customers, then it becomes an option to explore, but not if the whole product is available, always updated, in a pdf that everyone and thier cat can pirate.
What could also please the book buyers, is if WotC themselves offer a POD solution. Surely with their Hasbro connections, they could offer a $5 or $10 additional surcharge service to print out a copy and a few dollars for delivery. Or they could just offer it through Amazon and the like.
POD is expensive. You have paper type costs, ink costs, binding costs (cheap, perfect, or layflat among many options), cover costs (hard vs soft), etc. Publishers make money by ordering large print runs to reduce cost of printing. Wotc is not in the POD business, they are in the mass market publishing business. Offering products via POD also reduces Brand, as now you have cheap quality non-knockoffs that do not reflect the product proper, weaking the image of the brand to investors who expect some semblence of quality for a brand they invest in, esp if they are the big fish in the market.
As for gaming stores, well, I think they have to realise that markets change and that they have to change with them. One thing that I'd love to see WotC doing is to bring back the D&D miniatures game. The second hand market for D&D minis was awesome and allowed for game stores to sell individuals for a profit. Plus game stores who host games could run tournaments, which in turn helps sell more minis.
Enough ppl complained at random minis. Random minis were profitable. When the switch to combination of random and non-random occured, it was the death of the minis game. Add in increasing production costs, shrinking economy, thus shrinking audience with available funds to spend on your product, and as a company, you have to decide if a side product is worth hanging on to, or re-purposing. I'm guessing they had numbers from event reporting showing a decline in the mini game and projected it out into a flailing economy. If it wasn't performing well during a good time, it's not worth keeping on life support during a bad time. Taking a look at core product, it looks like the minis were kept on to support the RPG in a more limited scope. If the minis continue to perform poorly, i expect them to be cancelled all together.
Currently, the D&D minis are simply too expensive. I have zero interest in buying any of them based purely on cost. I know quality seems to have increased, but honestly, they're plastic minis, what I want is quantity, not quality. If I wanted quality, I'd paint my own pewter minis.
More for me

Wotc can't win here. To make quantity cheap enough requires reduction of production costs, which lowers quality, and then everyone complains about the quality sucking.
Improve the quality, and the cost goes up, and everyone complains about cost.
Only choice is to find that balance that moves product and puts money in the bank.
The point of all of this is that I think if they moved to a purely online distribution business model, that they could make a much larger profit, and therefore continue to put out good product, rather than filling the market with books that do little but sit on people's shelves. I would personally love to see the numbers on something like this, and the numbers on WotC's current profit margins. I'd be willing to bet they're making a loss on the hardcopies, and that their profit-leader is DDI.
Of course, I'm using WotC as an example as that is the company I know. But feel free to talk about other companies and examples of online vs. brick'n'mortar success/failures.
DDI may very well be a long term plan to buffer the bottom line, but you can't rely on a subscription model. During flagging economies, among the first to go in a penny-penching family is unjustifiable monthly expenditures.
MMOs, paid website subscriptions, netflix, etc. I've had to cut a lot of such things myself.
Meanwhile, a physical product, you've already sold it to distributors and made your money. It's up to them to sell it w/ markup and make thiers.
Additionaly, we often forget on these forums that just because *we* take computers as ubiquitous, not everyone has a computer, or if they do, are unwilling to buy something online. There are several at the flgs i play at that don't have email, yet play DND and PF. A lot of products I wouldn't even know about if I didn't see them in my flgs and thumb through them.
Don't get me wrong, I think there is definately a space for what you want, but it's not a very big one in the market (just very vocal on forums), and the investment to even experiment, let alone profit with that space is very large. Is it financially practical? I'm guessing people with a lot more research behind thier belts than us look at this question at least once a quarter.