I can definitely see how a 4e won't be for everyone. Particularly folks who really got into D&D at 3e and have already felt the pain of the 3.5 fiasco.
The more I think about this, though, the more I believe them about no 4.5 edition. Sort of.
See, the key for WotC is that they need to make money, like any business. And, ideally they want to do that in an even way. A level revenue stream is hugely better than one that spikes every 3-5 years when you release a new edition of your product.
They are attempting to do this with the DI stuff, and trying to find a way to provide enough value there to get a high % of players to commit to the monthly fee (I'm waiting to be convinced). They are also doing this by creating the online 'parallel' version of the source books. They have already stated that any errata will be 'automatically updated to the electronic version of your book'.
What I see this meaning is that they will continue to tweak the game, but in smaller more incremental steps than 3.0 to 3.5. Instead you might see rules adjustments and errata a few times a year. Your hard copy book will slowly get out of date (how much? depends on how good a job they do with the first release), but you will have the online version that stays accurate.
As time passes the DMG, PHB, MM will run through initial print runs and the newly published versions will incorporate the errata, having new covers indicating such. They will still be 4th edition D&D, they'll just contain different contents in some parts than the earlier publications. Meanwhile, the steady revenue stream from the DI means they won't push so hard to get people to buy the updated books, I believe they will genuinely try to keep the desktop electronic versions as useful as possible. Subscribers is the key to their future, not the book sales.
This of course means that folks with limited computer access get a bid screwed over. I hate to say it, but in another five years D&D will be becoming the least of the concerns for folks in that area. No need to derail the thread on infrastructure issues, suffice it to say I think it is reasonable for WotC to take the general approach I see, but can certainly understand how individuals would be upset.
Of course this is 90% speculation on my part. I am mostly applying what I see from other industries that have shifted from (or are shifting from) a purchase to own model, more to a subscription model. At first I was concerned, but based on what I see, I think WotC is being pretty reasonable about keeping it purchase to own, but trying to sell the subscription. Where they could lose me in an instant is if players need the subscription to get the latest errata or access all of information they need to use the base books at their tabletop.
