45lbs is 45lbs.
sometimes weight FEELS different because of how its distributed.  like if you're benching 225lbs and you have 2 45 plates on one side, and 9 10lb plates on the other side...one side will feel heavier than the other.  also if the bar is different than what you're used to.  i've never heard of someone having a 45lb discrepancy like that tho.
sidenote:  i remember the day i hit 135 on my bench.  dont remember 225.  will definitely remember 315 once i get there (maybe this year)