I could simply say "it doesn't have buttons, how can you play a decent fighting game like Street Fighter?" but no, I won't do that, instead I will say that Apple doesn't have a big support from bigger third parties (Square Enix, Level-5, Atlus, Capcom etc).
Also, the DS and the PSP has something to make them more representative as a portable gaming device, something to characterize them and make them even more strong than the Iphone could ever be: big first party games
My answer? Of course not.