I used to chair a committee for a postgrad conference. It was actually funded by the bigger affiliated (i.e. 'proper' ) conference so it really was about showcasing postgrad research and encouraging people to get used to presenting and I think it tended to make a loss most years!

The conference I've been referring to is not a postgrad conference and considering what they're charging and their costs, room hire, food, etc, I really don't think they're on it JUST to make a profit. I believe it is about getting people's research out there and networking... shame it's not my field:-(