Companies opt in to sites like Expedia and list their properties/flights/vacations on their marketplace and they pay a commission for those being booked. Expedia doesn't just crawl them and demand a royalty for sending them traffic...

Google has a huge pay 2 play problem with PPC... i've worked for Expedia so that's the only reason i know this :)

It's the reason companies work with Expedia many times because they don't have the leverage expedia group does...

i see it as unnatural change btw... "borg" if you will.