People need to understand iphone is more targetted towards business people..
Thus apps such as Stock, Map, Mail, Notes, Phone, SMS etc..
Ipod has always been about entertainment, music!
ipod Touch is focused towards people who want the next gen ipod, its a music player and music video player, ofcourse you can watch tv shows too
Due to the addition is wifi , safari was included and keeping in touch with the entertainment genre, youtube app was included too.
Though, because there is wifi and because there is space left in the main screen, i'm sure you can download apps in the future..Mail, Weather, Games etc