XBox Live might be a huge business coup, though. If you go to the trouble of paying for Xbox Live, you're gonna want to "make the most of it", and that entails doing things that make Microsoft more money (buying more monopoly money from them for downloadable content, buying more games, etc.)
I used to play quite a bit on PCs. Multi is generally free, but the experience is far from seamless in a lot of cases. My impression of Live is that It Just Works. I've heard very varied things about PS3 in comparison, many of them not kind. That's what I was drawing on.