WOW, I am shocked to hear that this is so prevalent. Reminds me of that Friends episode with Ross and the retiring handyman - and the whole point of that episode was to show how ridiculous it was. I would never contribute to something like that - sort of undermines the intent behind a GIFT if you are obligated to contribute.
We have a pool just for the women attorneys at our firm. But each year, an email comes around saying how much money is in the fund and asking if anyone wants to contribute. It is completely voluntary and doesn't impact whether you get a gift or not. I have gotten 3 gifts from them - one for my miscarriage and then twice for my kids. Then whenever we have a shower or something, we take up a local pool - but again it is completely voluntary. We send around an email asking who wants to contribute and how much they want to contribute. Once we know how much we have, then we pick the gift accordingly.