It's the old Chicken or the Egg question from Mike Mearls' post on Monday.
Mike stated the following: Traditionally, D&D editions have focused on specific play styles. This approach has fragmented the community over time.
The way Mike states the issue, he puts the emphasis on play style dividing the D&D community. That is a cheap ass punt if there ever was one.
The reason for the divisions in the D&D community lies primarily with the release of multiple editions. It's not just an issue with D&D, it's an issue with many RPGs that go through "Evolution by Edition".
The idea generally is as follows - to make sure people by into the new edition, you have to make it close enough to it's predecessor that folks recognize it and feel comfortable with it, while at the same time making sure it's incompatible with previous editions, thus ensuring mass purchasing of new products when released.
By making the old incompatible, you are making it obsolete. Or that is the goal of the publishers of games that follow this model. Which would work fine, except that orphaned editions don't need support to retain a significant portion of it's base. RPGs, by their very nature, allow for and encourage home brewing. If I can write my own (or these days find on the internet) adventures for my favorite edition, I have no need to move on. I also have no need then of your new edition products.
This happens with the release of each new edition (and the orphaning of each old edition).
Does Mike really expect players of 4e to abandon a game that they enjoy, that they already have a near endless supply of support for, to play a new edition that very likely won't be much like the one they are playing now?
How about the OSR folks? Are they going to leave their systems that are supported and very much alive for a new system that won't match their style of play?
Maybe the Pathfinder players are going to leave behind their amazingly well supported game to play a similar but incompatible game?
The answers to all of the above? I doubt it.
It's not the style of game play WotC is up against so much as the amount of support the other flavors of D&D already have.
The previous editions aren't dead. The OGL breathed life into everything from before 3x, and has kept 3x very healthy in the body of Pathfinder.
D&D Next has to compete against shades and dopplegangers of it's own past. It better be happy with scraps from the gaming table, because that's all it will likely find in the end.