This is a tired old argument, but Blizzard poster Vaneras wanted to drive another nail into the coffin by stating, simply, that Blizzard has no plans of launching classic or pre-TBC realms. Aside from being a very complex endeavor that undoes a lot of class balancing over the years, the game simply isn't designed for Level 60 content anymore. Still, there are some proponents of the idea, which has even gotten some enterprising folks to set up private (and illegal) servers just for vanilla WoW.
It's a line Blizzard has drawn from way back when, yet suggestions or requests for classic realms continue to pop up on the forums. Let me tell you here and now... don't bother. Blizzard will eventually just lock your thread or delete it entirely simply because it's not in their best interests to provide such a service. First of all, so much development time has been invested in moving the game forward. Blizzard is also ramping up leveling time because they want players to focus on the endgame that they're developing right now. Besides, really, the game has never been more fun.