That would be my guess as well. The alternative is far, far, far too much of a bombshell for it to be released in such a "drive-by" fashion.
That being said, I've had a suspicion that since the beginning of this difficult (to say the least) endeavor there may come a time when the effort to synch the large number of 2nd and 3rd order interactions of each of the core elements plus modules becomes so unwieldy that they just throw up their hands at the futility of it...and market basically a tight, Moldvay Basic type core game with a few minor dials.
That would not surprise me if it happens, but I'm all but sure that this isn't it. Its too terse and vague. If I was a cynical internetian, I would almost say that Mearls is laughing right now. Either that or facepalming.
Well, it isn't IMHO a 'drive by' of anything. They have been backing down to this since they first began to hint at DDN. The first talk was grand nonsense about a game that could be played in different styles so it would please at least the vast majority of D&D players regardless of if they liked OD&D or 4e. There would be 'modules' that would rework the various subsystems in order to achieve this.
Frankly the first post I remember making on the 4e forums can be summarized as "bunk, this is impossible, Mike and Monte are sniffing glue or shining sunshine where it doesn't belong." Everything that has happened since then bears out that analysis. Every announcement has steadily ratcheted back expectations. No, no, there won't be different ways to build a wizard, no no there won't be different skill systems, healing systems, etc and now we've simply reached the end of that long slide with "well, actually, we're not planning on having much in the way of options at all...."
Clearly what we are going to get is a 2-3 tier game where there is a 'basic' game, a 'standard' game, and an 'advanced' game. Each will simply pile some more options on top of what the previous layer in the cake provides. basic will be just classes and races, no skills, backgrounds, feats, etc. Standard will probably add backgrounds and specialties, and skills, establishing the default game. I'd expect Advanced will simply be a collection of optional rules you can add on top of that. Other things like domain management and henchman rules might also be designated as 'advanced'. There are NOT (and this has been stated) going to be ANY parallel options. There's not going to be a 4e-style skill system for instance you could swap in, or 'indie game'-like narrative control mechanics options.
The reasons you state, and additional nightmares in the production of adventures and supplements that have been noted a million times in the last year, clearly are too significant. There's just no way any game company could reasonably support a swiss army knife of a game like was hinted at 18 months ago. The real question, which of course can never be answered, is to what degree these unreasonable expectations were constructed and to what degree they were just foolish game designer fantasizing now brought down to earth.
Meh, whatever, I am loosing whatever interest I had in what goes on with WotC. 4 years ago I was their loyal customer and could feel confident in defending their good intentions, common sense, and vision. At this point they've squandered all of that completely. I only wish Paizo would publish a game that matched with my tastes, I'd love to be able to give them my money. WotC at this point is very unlikely to see any of it again in the foreseeable future.