Well, in my case, I like having a ton of DEs. I also like Linux Mint more than Ubuntu. I currently have Cinnamon, Gnome Shell, Gnome Classic, Pantheon, and Unity installed on my Maya partition. Just because I like Pantheon doesn't mean I'm going to move to Elementary OS. Just because I like Gnome Shell doesn't mean I want to move to Fedora. And just because Unity is more integrated in Ubuntu doesn't mean I want to use Ubuntu.
I love Linux Mint, and if I can have my DEs on Mint, then I am going to use Mint; out-of-the-box integration isn't something I really mind not having, as long as I have the tools and capability to reach that level of integration then I'm happy. Haha, that's me at least.
"Even a dead thing can go with the stream, but only a living thing can go against it." - G.K. Chesterton
Dell Studio 1555 running Linux Mint 13 Maya LTS x86_64/Windows 7 x86/Ubuntu 12.04 Precise Pangolin LTS x86_64