So selling a few boardgames is going to keep the business going?
Perhaps. I would have though that, overall, the market for boardgames is bigger than the market for RPGs - at my local games shop (Mind Games in Swanston St, Melbourne) the boargames are in the front, more visible area and the RPGs in the back area.
Whether D&D boardgames sell more than D&D RPG books I don't know, and I wouldn't know how to conjecture an answer either way.
The problem with this is, if they focus more on the brand than on the game then people will abandon the line and go elsewhere which could cause popularity with another brand.
If WotC does not publish many new RPG books, and there are people who want to buy lots of new RPG books, then it follows that they will have to buy them from someone other than WotC.
But the only game which is producing product at the sort of rate you are talking about is Pathfinder. Which, as [MENTION=6701829]Trickster Spirit[/MENTION] has pointed out multiple times upthread, keeps them well within the circle of D&D-lovers and D&D-players.
WotC seem to have formed the view that it is not economically efficient for them to try and chase those Paizo customers. On that, I trust their knowledge of their own balance sheets over anyone's online speculation.
They also seem to have formed the view that having some D&D players buy books from Paizo and play D&D under the Pathfinder label isn't going to hurt the D&D brand. I'm inclined to agree with Trickster Spirit that this seems reasonable. PF players play PF because of their love of D&D (the iconic RPG), not as an alternative.
Now if a game like Rolemaster or Runequest or Burning Wheel or The One Ring (just to name some currently available relatively well-known fantasy RPGs) took off, it would be a different thing. Those games are all predicated, in part, on being not-D&D. But much as I would love for some of these excellent games to get the commercial traction and brand recognition that D&D enjoys, I think the prospects of that are basically nil.
D&D is sacred to a lot of people and they would leave in waves than see their beloved game get put on the back burner more and more until it's an after thought.
It makes no sense that if the game is sacred to someone than s/he will abandon it. If it's sacred to people, they will value it. Which is what WotC is hoping for - because that valuation of a private intellectual property monopoly is precisely what the commercial value of a brand is built on!
All the while, we are getting a crap release schedule while they test out their newest hair brained theory.
I'm pretty confident that WotC has accountants and financial managers on its staff. They can read a balance sheet. If they've worked out that supplements aren't profitable, you're not going to see them. If the brand strategy turns out to be "hare-brained" then the upshot will not be supplements instead. It will be Mearls and/or his colleagues gradually losing their jobs, and the 5e publication schedule slowing down further.
Or, alternatively - and to allude to a post by BryonD a page or so upthread - they will try and make a quick buck off 6th ed.
Which is also pretty much true of WotC/Hasbro or any other company we talk about here. I think it's fine for us to speculate and conjecture, as long as we realize that is all it is. Without true inside knowledge or access to any company's financial data, we are all just guessing.
Hasbro is a publicly traded company. It's financial reports are public documents, from which people on these boards post extracts from time-to-time.
As far as I know Hasbro is a profitable company, though like all companies it wants to increase its profits. In recent reports WotC has been identified as a distinctively profitable segment of the company, and D&D has been called out as notably contributing to WotC's profits.
There is no reason to think that WotC is in financial trouble, or that it is not happy with the performance of its D&D division. Though it is true that, as far as I know, we have no real way of telling how big a part of that division's profits flow from the RPG.