Frequency throttling for a device where power consumption is critical (such as a laptop in battery mode) is a must have capability for all sorts of processors for years now. However I don't think anyone is as naive to fire up a demanding 3d game on a laptop when it's in battery mode heh.
Anyway I haven't the slightest clue what AMD's power saving features exactly include, but I'm highly sceptical if any throttling is going on while under full load. Probably not directly connected but I have AMD's Cooln'Quiet stuff on my PC disabled. That's what proper device and case cooling sollutions are for, and while those slightly add to the cost any processor won't throttle when it feels like it (relatively speaking) and yes there are massive heatsinks available for both GPUs as CPUs with 0db noise.
Before someone says that such sollutions aren't ideal for overclocking, any software driven frequency throttling isn't exactly either.
In summary since power consumption is way more critical in the notebook/laptop market, we'll have to see which of the two IHVs came up with more effective power saving and lower power consumption for either RV670 or G92 based mobile GPUs.