Also, please take time to read: http://conversations.nokia.com/2010/...-all-the-faqs/

That article is about the N8, but most if not all the techical stuff is the same in all Nokia camera phones. All the software related decisions that were made in creating the software for ex. the N95 (sometimes producing 'nicer' images) would be huge problems in re-creating software if the camera of the N900 would be exchanged. So, it just wouldn't be practical.