Making money via advertising while losing money on the deal…

I am flying to Washington DC tomorrow to attend (and speak at) the TANA 2007 conference. While I was booking my car rental at (Yes, I work for a startup) I saw an ad for  Here is the image

Of course, the price at HotWire was cheaper than and I had no choice (again, I work for a startup) but to book my ticket with

I really don’t get it. Unless and are owned by the same company, it does not make sense for to send me to a competitor site. Yes, they made money through advertising but lost money on the deal 🙁