I think one more thing about Maemo is the hardware.
You control it. Nokia WANTS you to do with it whatever you like.
It's your device, you paid for it, you control it.

To do the same on an Android device, you've got to root it (and this is illegal, AFAIK). Same happens with the iPhone. You've got to Jailbreak it.
Again, illegal.

A Nokia tablet is yours and you can choose to run whatever you like on it.