I’m just speculating here, but perhaps the iPod in the name iPod Touch is suggestive of a direction that the future iPod line will eventually take, so they want to retain the identity of an iPod versus a full-featured communicator (iPhone).
It just so happens that the iPod Touch is only the first (in the line) of iPods to include the internet and wifi-based features…as a mac geek, I’m willing to bet future offerings of the more diminutive models will eventually include the wifi radio, and have some sort of touch-based interactivity beyond the touch-wheel.