I don't know why the thread title says geeks AND newbies, surely you mean geeks NOT newbies.

Anyway, I think the reason is that although the N900 looks at first glance as easy to use as iPhone or Android, whenever anything goes wrong, or whenever you have to do something advanced, you might have to use the terminal or other things that might seem obscure to non-geeks. Personally, I wouldn't have it any other way, but I can see people put off if t.m.o every day when they're told to use the terminal or install a .deb.