Food for a table of 4 = enough food for exactly 4 people.
Food on a buffet = enough food so that people may overeat, have a full looking buffet throughout, and especially, enough so that if a majority eat the chicken instead of the beef, their needs are met.
Because of this, more food than is actually expected to be consumed is prepared and presented.
Desserts may fall in a different category if exactly enough are prepared.
But again, if there is an assortment, there will probably be more prepared than the exact headcount of the group, because you don't know exactly how many will choose the chocolate moussecake and how many the fruit tart.
In that case, these desserts won't be traveling either.
I had a party that had Baron of Beef.
We had to carve into a second steamship to meet the guests needs.
At the end, they wanted the 50 pound roast to take with them, and I declined.
Their position was that they had payed for all of the food prepared.
My position was that they had paid for all of the food they consumed.
They left without the roast.
Besides, I didn't have a doggy bag large enough.
:D
The safety issue is the reason most often communicated to the customer.
The reason I explained above is the true reason.