[Endrance]

Hardcore gamers partly depend on casual gamers to pay the upcoming patches and expansions for them.
And if you can really only play a MMORPG once or twice a week for 1-2 hours... personally I wouldn't even bother playing MMORPGs.

Also, F2P games kinda already offer casual gamers an alternative. But as you can see - the less money they get, the ****tier the game will be. And I personally don't find 10-15 bucks a month too much... even for playing just one hour a day. I mean... x1 disco or theme park is already more expensive than a MMORPG for one month and it's just fun for 1 day.
But yea, as I said - Playing a MMORPG that rarely pretty much isn't worth it in the first place.

EDIT: Misread your post. Playing 10 hours a week are worth $15.