It's either that or the fact that a new friend can't even reach the full potential of their spec until 80 (reach bottom of tree at 69, get mastery at 80) where as previously they could (potentially at least - bottom of tree was reached at 60 and there were very few spec defining spells after that - key word "defining", not just rotation adjusting). Also DKs start at almost 60 and they were considered WotLK content so Blizz wanted that to remain slow. Blizz has really moved a lot of game mechanics (badges to points, talent trees, spell distribution, etc.) to being pre-cata content vs cataclysm instead of a game with 3 separate expansions. It's just really hard to justify any vanilla only or BC only guilds with the current game mechanics. I wouldn't be surprised if by 4.3 we see a condensation to get vanilla + BC + WotLK in one software package.

tl;dr - Lots of reason to raise to 80. Subscriber numbers are probably just one small part.

As reasonable as that sounds, it's also something you hear just about every time Blizzard does any kind of promotion, giveaway, launch, perk, or special event. Blizzard is doing/changing/implementing/modifying/promoting X because subscriber numbers are going down the toilet and they're trying a cheap X to save the game.

Not only that, but didn't the instance servers max out last week (for the first time since what, 3.2?) with the new holiday boss? One would think that demonstrates an influx of players, not the opposite.