I think because we're not seeing many other uses right now, popular device support is a big deal, and like we saw with USB2 (and even 1.1 to some extent) even though USB may not be the ideal format for things like A/V, plenty of devices eventually came out for it, just 'cause it was so popular.
I see thunderbolt as a great way to finally separate the computer completely from the Display & I/O. Imagine an iMac-like doc. It has all your ports, card reader, webcam, even an optical drive. Your mac though, is just a completely sealed box. It only has two ports: a power plug, and a thunderbolt port. Pro versions might have two ports and a video card slot.