The one thing that I do not understand about iPod touch is the lack of Mail. Apple’s email client would run just fine on iPod touch… just as well as it runs on iPhone.
Leaving out other iPhone applications is actually understandable, for transitory reasons. Apple’s Notes application was not iPod-compatible… it did not work with the existing iPod Notes format. Apple is probably re-writing Notes right now, in order to support file system access and iPod/iPhone interoperability (not to mention the need to be able to download iPhone notes that you’ve written on your computer). Same goes for Apple’s widgets… if you’re going to add support for Dashboard widgets, those are probably all being adapted for the new Leopard Dashboard framework that will bridge iPhone, iPod touch, Apple TV, and Mac widgets. And for Google Maps… it’s a mobility application. An iPod user generally doesn’t need it (though still, Apple, it would be nice to have…).
The only conclusion that I can think of is that Apple is keeping Mail in reserve. It can be used to bump people up to iPhone purchases… unless complaint levels get too high. If too many people complain, Apple can simply add it back to iPod touch in a future software update.
It wouldn’t surprise me at all if people don’t come up with “Mail for iPod touch”, similar to how I came up with Mail for Treo 600’s, after only select Treo units came with the application (Palm later did-the-right-thing and offered CDMA units the Mail app, so I pulled the hacked copy). Essentially, the Mail app on iPhone can be packaged up, and deployed using something along the lines of AppTapp. Barring any protections from Apple, either your feedback, or clever hacking, will win the day.