There isn't any great diversity in Linux distros interface-wise. You basically have a handful of distros that use X Windows and one of the four old window managers.
I appreciate that. I agree it's not obvious what, if any differences exist between alot of the lesser-known distros. However I would argue that a large enough sample from the most popular Linux Distros has something substantively unique to offer.
But we haven't even considered BSD-flavor. Perhaps if we expanded to include BSD-based operating systems. To name a few: FreeBSD, DragonFly BSD, PcBSD, NetBSD, OpenBSD.
All of the BSDs mentioned above have a very unique mission.
It's easier for me (as consumer) to choose any one of those to run my desktop / laptop knowing that I'm going to pretty much get all the same access to apps that I would if I were to run Windows or OS X.
Without any reassurance that I'm going to be able to do what I need to do on a BSD or Linux machine, I'm probably going to be stuck choosing something created and maintained by Microsoft or Apple.
