[buran77]

Determining how much is in use out of what is practically available is relatively easy. But determining what is 100% is still difficult to decide on, CPUs have too many frequency options to decide what the "real" 100% point is. Even picking the base frequency as the reference would be a pain to properly monitor and predict, and to take decisions based on that.

[annoyingnoob]

Its more about determining what throttling means, 100% for conditions. In any case, the tools we are used to using have traditionally showed a percentage scale of usage - seems like a reasonable measure even if its hard to measure.