Really? How so?
Taking shots after the round is a DQing offence, not DQing him was an "on the fly" decision -- twice.
And while the normal rules is "1 lb allowance" for regular fights and "no allowance" for championship fights, there are exceptions to that rule:
So the rules were followed here as well (assuming GSP and/or Diaz were actually over the 170lb mark, which has yet to be shown, unlike the cheap shots, which there is no question about.)
Rules that Diaz got away with and no one seems to care:
But let GSP "abuse" a rule that is actually more to the benefit of Diaz than GSP (if it was violated by only GSP or at all) and guess who gets flack?
Yes, and the ref saw it and warned Nick. Case closed.
And I don't see how the rules were followed if they actually weighed in over 170.0. The rules you posted don't say anything about a WW championship fight being contested at 170.1 or more.
The other rules Nick broke were all inside the octagon where it is the ref's job to take care of them. If the ref didn't think it was against the rules then that's that.