Simplesally... that's a definite possibility. But I'd think that if the WTS can negotiate to have the concessions closed, it would certainly be easier to negotiate to have their members allowed to bring food.
freein89... it's a tax issue, just like donations for the literature. Sometime in the early 90's, the convention food was put on a donation basis. That only lasted about a year or two... obviosuly, the Society was not getting enough donations to make it worthwhile. So they just ended food service at assemblies, and declared that everyone should bring their own food. They also decreed that you have to bring it with you in the morning... you're not supposed to go out at lunch to get it. But that rule is commonly disobeyed, of course.
Matty... that's interesting. I don't think the stands are left open at any conventions in the US; but I'd be interested to find out if I'm wrong.