De La Hoya weighed 160 for the Sturm fight and looked overweight and pudgy. 155-156 was a natural, in-shape weight for him at that time.
Bernard only weighed 157 (or 1 pound more) when he fought Trinidad in '01. He weighed 158 at other times. Hopkins had plenty of fights where he came in well below 160.

The Hopkins-DLH fight was a legit 160 pound middleweight championship fight. There was no clause regarding a reduced weight limit.