I own a July 2011 MBA, the lack of USB 3 on this machine & the lack of affordable TB portable solutions at this point is a sore point with me. Yes, I like my Air but do feel that if Apple wanted to release a notebook that featured TB & did not include USB 3 on a machine sold to consumers that they should have supported TB & made sure we had an affordable external drive to be able to use it. A 3rd party device that's hot, heavy & costs over $400 arriving almost a year later is a big fail IMHO.
They did release the Thunderbolt-to-Ethernet adapter, and have a Firewire 800 adapter planned. My guess is that Apple was waiting for the peripheral manufacturers to fill the market, but then when they didn't, decided to enter the market themselves, particularly because they knew they would be releasing a MacBook Pro that lacked built-in Ethernet and Firewire. However, the new MacBook Pros already have USB 3.0 ports, so there is less incentive for Apple to release an adapter themselves.
That said, now that Apple has shown that it is possible to produce and sell an inexpensive adapter for Thunderbolt, maybe others will finally come out with cheaper solutions.