At the end of this interview with Bill Gates, there's a question about Microsoft's music business. The answer is interesting. Apparently, MSN Music is about building relationships with a "critical mass" of consumers in order to be a player in future e-commerce of all kinds.

We wouldn't do any one isolated category of sort of online digital buying by itself, because we believe in having essentially a digital payment system at critical mass that works in all the countries. We're investing in the platform to do that, and at some point, we'll apply that to things like music, and so it's part of a broader strategy.

(Off the top of my head, I think there's more money in music than in avatars or "the right to send SMS messages," but I guess that's why he gets the big bucks.)