well i know a few former CFL players personally that have told me this happens in football a lot... the reasoning i've never really understood myself, but you're asking me to know what somebody else's motivation is, which is kind of impossible... my *guess* would be that they want smaller players to look bigger on paper so that opposing teams don't take advantage of a smaller/bigger player matchup (ex: a small CB trying to cover a 6'4" WR).... this doesn't make any sense to me, as other teams would know about this on their own, it's not like they are checking the official stats or anything when deciding on matchups.... like a said, it doesn't make any sense to me, but that doesn't mean it doesn't happen.... i know it does
as for the NHL, my knowledge isn't as direct, it is second-hand... ie: i know people who know NHL players who have said this happens... if you check my post history, you can probably guess which exact player i'm talking specifically about... the lie in this case wasn't making the player bigger, it was actually to make him weigh less (pretty big hint there if you know my post history)
if that isn't good enough for you, then well, i don't really care