Sorry if i sounded snarky Allisonwonderland, personally if it was up to me I would ask as sometimes there is so much cake left, but apparently its just "the way its done" and they (the powers that be) don't like for you to rock the boat by asking. Seems to me like a simple request, but that's they way it is...
So much food is thrown out from a catering place, you wouldn't beleive it...it seems like such a waste but you have to follow their rules or listen to it

. We can't even donate leftovers because the soup kitchens can't take it under some kind of law, so as to protect people from getting sick from improperly stored food. Its sad but true that the catering halls throw aways of this country could probably feed just about every hungry person in the country but the logistics just don't make it possible.
The best you can do is pass along the info, like thispost, so others can be aware.
PS: I had a woman once who had an extreme fit over her cake, wanted my boss to fire me because it was so "special) (sweet six, 3 tiered cake, very very little left over) she ranted and cried, saying her "heart was broken". If it had been so important, she should have provided the information and a box to wrap it up. I felt really bad for her, offered to pay for another cake, but her husband said it wasn't a bit deal...then she called my boss AGAIN 10 days later moaning and groaning so he sent her a certificate for another cake, which I had ALREADY offered to take care of...No problems with the boss, because I was just following his instructions on the cake, but I felt bad for her just the same, tho she really was a wacko - the party was beautiful and it was justa cake for crying out loud. Not even half of the bottom layer was left, you would have thought i stole one of her kidneys or something the way she carried on,

too bad she ruined the memory for herself. I can see being annoyed, but really...
LL