> But the only reason that scalping is profitable is that more people want to go to these events at the original ticket price than there are seats available.

In general yes, however I have seen plenty of events that didn't sell out and scalpers where left still selling tickets and perhaps some people only knew about sites like ViaGoGo so bought of there.

I'm sure times when demand closely matches supply, it's still going to the scalpers because they get in there first.