Let's get to one MAJOR difference, Maemo on the n900 typically has around 100 programs that run simultaneously 100% of the time, and still retains a reasonable cpu/memory footprint and most importantly, the charge is kept around the same amount of time as an iphone.

Just about all other phone OSes go into a severe suspend state when the screen goes off.
It takes mseconds to get out of this state.

This means it's impossible to create normal software that does anything useful unless you're holding the phone in front of you.

IM software, GPS tracking, any kind of server etc. all become impossible unless you marry it with some weirdo API that may or may not exist on that platform. And even then, you get races, security and stability issues which cannot be solved with such an OS architecture.

(This was also the reason why some of the Android patches have to live outside the mainline kernel)

Only one of the reasons why Maemo, runs the same software you run on your home PC, while none of competition can.