I'm with the crowd that says there is no way conventions/assemblies lose money. In my mid-sized city, we have an assembly hall. The rent for that is higher than what we paid for other venues before the AH was built. Granted, the facility is more user friendly in terms of layout, AV equipment, etc. But, it's not like they are losing money on it. I argue they are getting higher than market rates (or at the high end of market rates). Of course, they say some of it is for maintance and the like, but other venues would face the same thing. Plus, add on that they aren't really charging "rent" but rather the elders vote on the recommended donation based on the projected number of publishers assigned and you have a profit generating operation which DOESN'T PAY TAXES.
Now, on the international conventions, depending on the venue, I could see maybe some of them not turning a profit. Like some of the ones here in the US this year. It will be interesting to see if those cover the expenses. My guess is if donations don't, there will be a bill back to the individual districts/circuits to make up the difference.