Yep - it's 100% software. I don't think the US has any regs against ad-hoc WiFi specifically; what I heard a few months ago was that the cellular connection + an ad-hoc WiFi connection together put the phone as a whole over the FCC limit for RF radiation. This doesn't seem to be a problem for any non-Nokia phones, so the real reason is probably that Nokia doesn't take the US market seriously enough to put in a real solution and not this half-baked one, which is just enough to get approved.