All depends on the price point. If I was buying a new machine at retail price, then yes, I'd expect it to have USB3.
But I think I can spend less and confortably survive without USB3 for a while. I can use FW800 or thunderbolt for storage, and if I really need USB3 I'll get an adaptor.
Also, tech gap is only important if people change their desktop PC every year or two. I'm not sure the majority do. I expect to be happy with the current iMac, and see a couple of refresh cycles occur before I buy again. Perhaps I'm in the minority but I don't always want the new shiny thing - I want something that works for me and does what I need. If it does that then the newer shinier thing is all well and good, but I'll only buy it when it add reals value to me.