There is no such rule. Most likely it is a custom, part of the corporate culture for the particular organization. Some companies constantly lavish food on their employees (particularly startups operating on VC, thinking they can afford it—hey, guys, all those free Tuesday lunches and Friday beer busts are going to add up to one or two of your jobs in another year or so), but not all consider this extravagance a good use of resources.
I work at a large and highly profitable company that has banned all catering except for customer events. If there are muffins and bagels at a two-hour division all-hands, the VP has paid for them himself. But even before this, food was not the rule unless it was a special event.
We do typically bring water bottles along, but as soon as they remove the bottled water coolers from the break rooms (yet another impending take-away), I guess we won’t do that any more.