However much noise they make about bringing in new players, WOTC has to know that the market for 4th Edition is almost entirely existing D&D players. The recent obituaries for Gygax were very telling in this regard. Almost all of them that I read spoke about D&D in the past tense, as something that created much of todays' culture but which is not culturally important itself anymore. Much was said about how World of Warcraft wouldn't exist without Gygax, but I can't remember a single mention of an upcoming 4th Edition in the mass market press. D&D, as far as the wider culture is concerned, is something that stopped being important in the late 80s.
I recently bought some dice in the local game store, which is really a boardgaming/Magic the Gathering club with with a retail operation. The guy operating the register asked me "You still play D&D?" I had to tell him that yes, there really were people that still played PnP RPGs. He thought it had completely died out. I can't personally name anyone I know under the age of 30 who plays D&D, and I know plenty of people in their 20s.
New players simply aren't coming. Few of us want to face up to that, but we are part of a dying hobby. When the last time you saw an ad for D&D anywhere but the geek press? Nobody but the existing player base knows or cares about a 4th Edition of D&D. In fact, most of the actual player base (who don't read the online forums and don't go to Cons) neither know nor care about the 4th Edition.