I don't know. If it were around 50$ a year, it came with a certain number of wii points per month (basically, free VC downloads), multiplayer on games like MP3 with voice chat (to better organize squads and get the real war experience--with all that pesky dying), and maybe even some movie rental options/bonuses (obviously, the Wii would need some storage upgrade, USB like for that to happen), the it might be worth the cost of one game (50$). Add to that, what if the Wii got a Second Life-like game, or a WoW-like universe. Online play can dramatically extend the life and fun of a game and it's worth.
I don't know all of the Xbox live features, but I've never heard any users complain about the price.
Nintendo has one strike against it with it's cumbersome friend system (which I still don't fully 'get'). It's not a fatal strike or anything, but they need to make the system convenient for users (bypassing the friend system with some sort of adult verification system for instance, use a credit card to prove you're an adult, and you don't need Nintendo's 'protection'), especially if they start thinking about charging for it.