I think I have an argument-ender here, though i take no credit for it.
The version that was playtested, besides being pre-alpha, was also the "core" version. They stated that by "core", they don't mean much "the only official one", or "the only one you get to play without splatbooks". No, they said it's the "basic foundation" of what "basic D&D" is, and on top of which every play-style can be built. Now, it's more than logic that the core ought to be the simplest possible, hence the old-school feel. It's also more than logic that 4e is the farthest thing from a "basic D&D experience", not because of the fluff which is subjective, nor because of the different "feel" of mechanics, which again is subjective. It's just objectively more difficult to pick up: you have way more options at 1st level in 4e than you had at 4th in every other edition. As such, it's obvious that the "core" aka "basic" game, caters less to 4e than it does to other editions. That doesn't mean that the "4e module" (aka Tactical Combat) won't be on the very first Player's Handbook. What's more, you can be pretty sure we'll have it from the start, because as many others said, it's not in their interest to loose 4e players. True: players wanting to play 5e in the 4e style will have to tinker more with the rules. But that's exactly what they've been doing with 4e for the last 4 years. And again, those rules are going to be just as official and valid as the "basic"/"core" ones. They're going to be Core in the actual sense. As Mearls was quoted saying more or less, you'll be able to play your 4e-style character right at the side of a player who'll play a 1e-style one. They'll be balanced, it's just that the 4e one will have many more things to choose at each level, compared to the others.