As was mentioned, I think there is more than enough room for both games to exist side by side. It's not like people will suddenly up and declare that this "role playing" thing is for the birds and exclusively play without a DM. In all likelihood, it will act as another gateway game into D&D, much like DDM does now.
Personally, I'd love to see it work that way. Imagine a newbie player sitting at your table that has gone through DDM. You don't have to explain 90% of the rules to him. He knows how combat works. He knows how AOO's work. He knows which dice to roll. That's a very well trained newbie.
I'd much rather that at my table than someone who is coming from an amateur thespian game and figures that everything should be ruled on the fly.
I can also see how this could really help DM's who need a bit more time. "Okay, guys, I pulled double shifts this week, I didn't have time to prep, let's break out the Dungeon Tiles." Hey, depending on how it works, you could set up a Dungeon Keeper style game pretty easily I think.