They wouldn't dare charge for online gaming unless the game was released at a price of £25 or less as a RRP (not £50).
But they are trying to make more money from their franchise in the long run.
Whatever happened to that lawsuit of theirs where they tried to get MS to give them some of MS's profits for X-box Live considering it was MW2 that was the most played game on the service? EDIT: Reading above I presume they got some, they should have just asked for a little percentage based on number of CallOfDuty players instead of a lump sum. Unless they do get that?