Lets start:
Does iphone and android phones can boot 2 or more os as N900 does?

Iphone and android win in game section, but don't forget. u can boot nitdroid for android games and preenv for webos games on your maemo, and if dalvik comes android will be in maemo.

Can they use h-e-n app? Use usb and hard disk on NTFS? N900 can do this buy installing Power-kernel thats all.

Can they use Dual shock 3? Can they use touchscreen amulation to play games on tv with dual schock 3?

Ofcourse newer phones have more powerfull processor-more ram-more powerfull GPU. N900 is 2 years old (or more) and with overclock to 1100mhz (stable for me) is more powerfull than iphone 4 and hd desire 2. Ram is only 256 on N900 but it use swap memory pretty good to work like it has 1gb ram - android and iphone don't have swap hahaha.

and much more.
Think of it. Maemo is LINUX-The most complete open source and hacking software. CSSU make n900 better than before after 2 years - only few phones survive after 2 years/.