That depends entirely on the size and nature of the company. The huge ones quite often take losses to lure people to them...
But most likely you are right, valve most likely still take a profit, just my point was that sale or not Beth get the same amount from each sale.
Yeah, it's just offsetting the costs slightly, say I bought something for 50p, and wanted £1 for it, but noone would pay that high a price for it, but they are willing to pay 60p on a sale, sure I lose 40p profit on every sale I make, but, likely, I'll sell a lot more at the lower price, while still making small profit.
My experience is totally different though as I don't deal in online sales, so I'm not sure how it works. I wouldn't be surprised if the above is true though.
Edit: I'm not really great at explaining it in writing to be honest, I hope you get the gist of it though.
To be honest, whether you pay $20 or $10 for the content, you are still supporting the developers as the money will wind back at them eventually. Not really though, to follow the money is tricky, essentially Beth already got their money, as Valve likely already paid them for it. (I may be wrong, as it's an online deal, but it works this way with distributors and trade warehouses. They make you pay for the goods before you leave. As I said, maybe Beth have a deal with Valve that doesn't follow this properly or something.) Kinda like a sale or return deal? Like magazines.