They're trying to break from the norm to make more money, if it's successful i wouldn't be surprised to see EA follow suit fairly quickly with a Sports games sub. It's the same as newspapers charging for online access now, they're all looking at the Times to see if it's a success before doing it themselves.
Don't get me wrong i think this is a stupid move but then again EA lost $82m in Q3 this year compared to Activisions $15m profit, so on a purely fiscal level they're doing something right. When you can make up to $2m selling a digital star pony in WoW then it's going to make you push the limits.
Just to make it clear though i don't like Kotick or Activision

so no nerd rage from anyone please.
At the end of the day none of the MW packs listed earlier in the thread charge for actual multiplayer access, it's purely for extras like customisations or leagues, you can still play and enjoy the game without spending a penny over the purchase price, as long as that stays the case then i don't really care what Activision do. Yes WoW may be more monetised since Kotick came along but all of that is for non essential goods, as long as that stays the same then i don't really see the problem. If enough people pay for MW2 subs to make it profitable then fair play to them really, but i won't be one of them.