I too always heard that it's bad to drink anything except water before bed PERIOD....but that milk/bottles due cause tooth decay as well. Thats why we brush our teeth before bed, so there isn't food on our teeth - same rule goes for kids.
I don't have a "written poilcy" for it either because I too thought it was just DONE that way. They can drink a bottle if they want before nap downstairs, we brush our teeth (all the kids) then go down for nap.
If a parent wanted the child to drink in bed I just wouldn't do it. I'd continue my way....but that's how I see things.
So what if the parent was insisting? Would you just not tell them? What about the transition and weaning from the bottle? They are GOING to cry for sure, do you let them cry? Do you let the parents know that's the plan? Am I just telling the parents too much?