Well, there's a little more to it than that. Consider that most WoW players already had multiple 80s by the time Cataclysm was released. Few were even doing old world content unless they re-rolled a goblin or worgen. Then consider that most re-rollers were probably veterans who just wanted to get their new character back on par with their main and/or guildies as quickly as possible. Add to this the fact that the leveling process for WoW is
so fast, especially if you used BoA items. I did make a couple of new alts with Cataclysm and most of the time I would outlevel a zone before I was even halfway through it.
The sad thing is that 1-60 actually was a lot of fun (the only enjoyable aspect of the whole expansion as far as I'm concerned) and they managed to make every zone worth playing unlike in vanilla where some zones simply weren't worth it. Unfortunately, it just came too late in the game to be appreciated.