Toussaint is exactly right -- this took me back. Way back to the original login screen and music, when level 60 was the max and everyone was running UBRS and the Plaguelands instances, and "heroic" was just something us players were. Even the Burning Crusade login screen, right, brings back some memories, of wandering around Hellfire Peninsula and raiding in Netherstorm. The roar of the frost wyrm we have now is nice and all, but sometimes we long for earlier days.
Which brought me to the question: what about a theme-switching system? There's no real reason the login screen has to be set to the current expansion -- while it's nice to have a new look to that interface every time we reinstall the program, there's nothing the new one really does that the old one couldn't. You'd think they'd be easy to change around, and if Blizzard just gave us a drop-down switcher in the options, we could choose whichever one we wanted.
Let's not forget, however, that their code is weird -- you wouldn't think that they'd hard-wire the new Battle.net login code to the newest login screen, but maybe they did something silly like that, which would probably mean we'll never see the "classic" login screen again. But still, if there's a way to do it, it would be nice to see that old portal and hear that rousing anthem yet again.