That isn't what he said in his comment. He said that he tested it under lots of conditions and couldn't see it go beyond 800MHz, therefore was confident (his exact words) that that was the maximum frequency. Not that it rarely goes over it, but that it never goes over it because it can't.
http://emkey1.blogspot.ca/2012/11/low-tech-acer-chromebook-unboxing-review.html
Read the comment section below. Also I find it strange that in Sunspider, how a 1.3GHz Celeron 867-using Chromebook gets 400ms, when that benchmark scales nearly linearly with clock frequencies. If the Acer C7 is really running at 800MHz maximum, it should be getting close to 650ms, not ~540ms.
I don't know why you think an Android or Chromebook device can't ever experience full load, even if only for short times. Just because these OSes can run on relatively weak hardware doesn't mean there are not times when the software wants to get something done ASAP.
TDP
isn't full power either. For mobile Core 2, the X9100 has 44W TDP, but it has DC specification of 1.325V in Enhanced Dynamic Acceleration(early form of Turbo) and 1.275V in High Frequency Mode, with 59A Icc. That's well over 44W.
For Ivy Bridge, the 17W chip has Max VID of 1.2V, and ICCmax of 33A. It also states Thermal design Icc, which is at 15.8A.
But both chips have advanced power management, which doesn't allow such figures to be sustained, making it a practical maximum for system design purposes and such.
For Sandy Bridge and Ivy Bridge, it specifically states Power greater than even peak power during thermal response time can happen for an extremely brief under 10ms.
So for TDP values, it only counts when its done under some sustained duration, which I pointed out few pages ago. If you have no application that is capable of reaching TDP values(the practical max power set by the CPU), but only does SDP, the latter would be accurate as well.