I think that you cant compare n900 to iphone. Just type to google ,,why iphone suck´´ and you will have your answer. Just brief example, you don´t have really multitasking on iphone, or cut and paste function etc...
And iphone is for customers which are not ´´tech´´ oriented, so wast majority of them don´t care about these things

I don´t have much experiences with android, but you really can customize nearly everything on n900, thats why it is called computer, and android has some limitations so it is smartphone