Conferences are lower margin than you think, particularly in tech. They're normally thrown for the good of the community or as a loss leader for some other business/product. If you're lucky, there's a slim profit that can be reinvested into the next conference, or that allows you to pay yourself for the insane hours put into planning. In all, tech conferences are generally a labor of love.
This certainly does not apply to conferences that cost a cool four figures to attend and are geared towards the corporate market. Nobody can tell me that the organizers are not making money.
Oh definitely -- Legal, Medical, Real Estate, "Corporate Leadership" -- those guys are definitely out for the payday. They also usually are thrown by niche publication/magazine firms, so there's even more to be made.
I think that's pretty typical for a conference the speaker would have attended anyhow. I've certainly spoken at conferences like that and been quite happy about it.