I love Android but I'm also a developer. It's not productive to try and write code on Android. I have in the past skinned my Gnome Shell to look like Android Holo (I just applied styles someone else created).

Much like bumper stickers or giving your hatchback racing stripes, it's a way that people can personalize their experience.

Also for the people who are designing the skin, it gives them practice interpreting/adapting the spec and some of that knowledge may trickle back to the source.