The weight bug was a mistake (major one) by the programmers. Instead of heavy guys being able to check and take checks from lighter guys, its backwards so that light guys (Theo Fleury) are wrecking balls and heavy guys (Marty McSorely) get knocked down easily.
I think the ratings in the game would be more accurate with the weight bug fix, as that was the intent of the game. At least that is true in 94, where skilled players that are heavy (Lemiuex, Lindros, Bourque) are rendered almost unusable because they get knocked down on every hit.