Originally Posted by
Spiralphoenix
It only diminishes relative to total DPS. As in, percentage increase. Haste does the same thing, haste is just inherently more complex with shot shifting/etc. so that is the reason why it is not so simple, NOT because haste "doesn't diminish in value". Any stat will do the same thing, the same amount of the stat will provide you less relative to your total DPS in higher amounts because just the basis of having the amounts before the 1% you are adding, your total is increased. In fact you can see the same effects doing the above in FD for mastery instead of crit. Each 600 provides the same amount increase, and a lower % total increase.
You can also see the above effects illustrated in the spreadsheet I posted above. The same thing happens for haste in a simplistic environment. Saying the real thing is not a simplistic environment is not a valid argument that haste does not behave the same way, it behaves differently because of shot shifting/focus regen increase/other more complex mechanics.