I would not doubt that at all. And I am guessing that a lot of them do not even realize it and/or notice it.
I have had several WS statements where my rebate was not listed, I called them on it....and their answer was they did not get it in time. I told them that was "wrong" and the mail system has way plenty of time to get it to them....and then they add it back to my account. Kind of like a credit card company that would add a finance charge because they said they did not get it in time....sooooo, now my WS statements and my one credit card payment get sent registered mail. BUT, to be fair, twice my bookkeeper screwed up and did not get it off in time (in the past 5 years)....and they have given me the rebate back with a phone call.