Really? There are a lot of people with Bluetooth headsets now. I'm sure they would love to pair that with their iPod Touch to also be able to listen to music... Don't know what percentage of people that is though.
{edit} I would predict that it's equally possible that there are a lot of users out there that don't care about Bluetooth on their phones either, but that didn't stop Apple from cramming it into the iPhone {/edit}
Ah, Bluetooth was just an example I picked from previous comment. iPod Touch actually has Bluetooth nowadays, it seems.
My point was that device manufacturers drop features from cheaper models because of costs. "This won't make a difference how many units we sell, drop it and we save $50 million!". Nokia does this all the time with their phones. From outside, it can appear as an artificial segmentation, but it rarely is.
{edit} I would predict that it's equally possible that there are a lot of users out there that don't care about Bluetooth on their phones either, but that didn't stop Apple from cramming it into the iPhone {/edit}