I don't have a thunderbolt device yet, but I wouldn't expect the behavior you're talking about. Being able to connect my old firewire devices might be nice, but I wouldn't expect to be able to use new devices on an old port.
There's no reason to expect it. But USB does it anyway, and it's really nice to know that I can buy USB 3 devices and use them with my USB 2 computers as long as I don't need top performance.
