Some jobs feed their employees, some dont. it seems like an odd thing to decline the food just as a rule.
Agreed. It's unreasonable to ask a vendor to devote an entire evening (and sometimes the majority of an entire day) to them and imply that they shouldn't eat. Doesn't matter if it's a band, photographer, or wedding planner. If you're on site for 8+ hours, you need to eat. And I'm not playing a 3 hour set with no dinner if I loaded in at 3pm.
I'm totally fine if the client doesn't want the band to eat the same food as the guests. Wedding and event food is expensive. But if the client can't be bothered to provide a deli tray from the local supermarket and a case of bottled water, then they shouldn't be booking bands.