I think you mean apps not functionality. As far as i understand about functionality (i could be wrong) it goes the opposite way. I haven't seen any functionality my iphone 3GS can do and my N900 can't. But a lot of things N900 can that iphone can't even dream of. I don't own an android phone so cannot comment on android phone functionality.
As a normal phone user, N900 can hold pretty well at almost anything i throw at it.

I still wish there were more cool games on N900 tho