1) think the differences between those shells are much bigger than between Luna and classic in XP

2) that it's a different shell, not a fully different desktop environment isn't really that important, for a normal user it will already cause confusion (maybe even more as it requires additional explanation what's the difference between the two).

Don't get me wrong: the thing that you have a choice is one of the virtues of Linux, but at the same time what it causes is that:

a) Linux is doomed to fail on a mainstream desktop market

b) none of the available choices is and probably will never be as polished as commercial competitors (and fragmentation is one of the reasons of that)