It's too smart to be a smartphone...

But seriously.. the real actual reason it's more of a mobile computer than a smartphone is the similarity with other Debian based OSes. No other platform has such similarity with a desktop OS.

Just create an issue with your phone. Then search for a solution to that issue for let's say..Ubuntu. It will 99% solve your issue too. Porting apps to Maemo from Ubuntu would be very simple since they're so similar. The problem is that desktop use x86 architecure CPU and the N900 uses ARM. If they both used the same type of CPU, we'd see a lot more desktop apps here.