It's an interesting question. Neth answers pretty tamely, saying that we were all noobs at one point, and that they want to make the starting areas as welcome as possible. But the question remains: is Blizzard expecting an influx of new players at some point in the future?
If so (and why else would they completely revamp the tutorial system and starting experience in a five year old game?), we have to wonder where they'll come from. Will Cataclysm bring in a swarm of new players? I'd think that it would bring some people back to the game, but I'd assume that most regular gamers have already played World of Warcraft and/or one of its many originators and imitators at some point.
The WoW movie is mentioned by a few players, and certainly that's a possibility -- though the movie isn't due out for a comparatively long time in terms of patches. Starcraft II may also bring a number of new players in or back to the game, as the new Battle.net system will definitely spread the word about people playing World of Warcraft. But even then, all of those new draws combined don't really seem like they're capable of generating the flood of new players that completely revamping the starting experience would deserve.
Unless Blizzard has something else up their sleeve -- something like WoW going partly free-to-play or a big boost to recruit-a-friend would certainly bring in a flood of new players, enough to justify giving them new tutorials and easier leveling. Whatever it is, Blizzard definitely thinks the newbies are coming. As with so much of this game, we'll have to wait and see.