Having a platform for multiple consumer products is a marketers dream, especially if it can give effective differentiation with economies of scale in production. The danger of course is that the differentiation is not strong enough to prevent the lower margin product lines from cannibalizing higher margin products. Of course, the challenge is to make sure that all products are attractive to at least some segment of buyers. Wharton runs all MBA students through a great multi-period market simulation that really drives this home.
The ability to exploit a platform is why the iPod Touch was inevitable. On its face, it looks like one of the best moves Apple has ever made. But when you look at what they didn't include, the picture changes: no email client, no microphone, no bluetooth. Think about that for a moment: an Internet device without email. Wow. I'd say that it's not really an Internet device after all, just an incremental feature on the iPod.
Folks, people buy the iPhone because it is a phone. People won't buy this in lieu of a phone. People will buy the iPod Touch because it looks like the Internet device it isn't and because the last generation of iPods break too easily. Hopefully, the next iteration will get it right, because I know a lot of people that want the device that they are marketing but not selling, myself included.