Well, TBC is now free.
World of Warcraft and The Burning Crusade -- Together at Last! - World of Warcraft:
In addition, anyone who owns the original World of Warcraft, regardless of when they purchased the game, will automatically be able to access all of the content and features from The Burning Crusade expansion at no additional cost. It’s time to set forth from Azeroth, adventurer -- Outland awaits!
The question is why. I mean, Matlocker, my alt account alt that I got to play a little refer-a-friend, is excited. I paid something like, what, $15 for WoW Old World at Xmas with a $5 dollar gift card back, so now I've gotten a month and an expansion for $10, which wasn't bad. I guess maybe this will convince alters and friends to run ten more levels o' fun, which takes another month or two. (Now Matlocker would like his free 10 days to try BC out. ;^D)
Of course this means that BC boxes in Gamestop etc now, if they're still out there, are worthless. Woe to those who buy. I hope they've pulled the SKU. Beware habitual eBayers.
I guess this is good in that Blizzard can get rid of one bit flag. Now everyone can hit BC. Still, I can't imagine that's a huge savings. Perhaps now they have one less client to test. That would be worth a bit of time==cash.
But are there tons of level 60ish characters running around who got Vanilla and stopped? Am I missing something? Though if we assume those folks wouldn't buy BC but will play a month if it's free (especially with a quick email prod), 1% of 11 million * $15 is still a lot of dough, I suppose ($1,650,000).
 Okay, okay, I know what you're thinking. A $5 gift card isn't worth a full $5! You're right. It's hard to spend a Gamestop gift card at Burger King. But if you're going to spend that $5 at Gamestop immediately anyhow, well, it's worth $5 to you.