I'll approach this question from a different angle. I give the following advice with the assumption that your buddy's wife is not a gamer, and not a Xbox 360 gamer in particular.
As a married guy (nearly five years, thanks), I'd say that if you actually want this to be a game console for both your friend and his wife, I'd choose the Wii; if it's just for him, you might go with the 360. Most of the couples I know who play games together play them on the Wii; since your friend likes old console games, then I'd throw in some Wiiware point cards as well.
When you get married, if you want to have a good relationship with your wife, it's just a fact that your gaming time is going to get cut somewhat. For many of my friends who like to game, the amount of time they spend on their consoles is a major point of contention between them and their wives early on. When you have kids, like I do, gaming time goes down even more (if you're not a completely worthless parent.)
So my advice is, give them a console something that will allow them to spend time together.
If his wife happens to like FPS's or just has a love for all things Microsoft, then just throw my advice out the window.