Yep, the performance tuning on the flat maps is done without the aid of the O2S. As soon as you exceed 50% load (MAP) or 70% throttle (TPS), the ECU goes into open-loop. The open loop operation ignores the O2S, and uses flat maps.
The O2S, in this sense, is only really checked when cruising, deceleration, or low throttle usage. The stock maps are poorly tuned enough once you start making changes, the throttle response gets really snatchy, and the low throttle usage performance is quite... Unimpressive. This, too, could be tuned, but it very fiddly and the O2S response sampling is slow enough that it's not going to react fast enough to facilitate smooth throttle response.
With regard to Cali emissions things, if they start integrating them in they'll either start at a) just ECU checks (I'll pass, no sensors to make me fail!) or they'll have a grandfather clause. Think about how many Harley owners (and there are a LOT out here!) would be up ****'s creek without a paddle if they don't do anything like that. =)
Overall, legislation is focused on other issues right now, since the last push for motorcycle regs didn't really go anywhere. And 'doing it right' is a reasonable risk in my eyes. But these are all just my considerations. =)