To Maked Speeds

I'm currently looking into Linux and Ubuntu has caught my eye. However, I've noticed that Xubuntu appears to be the same thing, but lighter on resources. If Xubuntu is so much faster, why is Ubuntu more popular? It doesn't sound like their are more features. Am I missing something?

Thanks, but I've already read the wiki. Basically there are two questions I have:

1. How much harder is Xfce to use, and does it have as many features?
2. How much slower is GNOME?