Ubuntu is all about the ease of use. How do you explain to your non-technical wife, for example, what a login manager is, what it does and why you'd want a better, lighter one? I like this change. I wish they'd switch away from Gnome entirely and go with something like XFCE by default. I want my DE to take up as little resources as possible out of the box.
Unfortunately, there are too many standard programs out there that need Gnome to run. I can't see Ubuntu using XFCE but still requiring Gnome installed; for newbies that would not be worth the effort. XFCE has a steeper learning curve than Gnome for people coming from Windows.
In some of the performance comparisons with Gnome, XFCE ends up consuming almost as many resources as Gnome. That's one of the reasons Lubuntu came into existence.
