Can you imagine if Google entered this market? They would give the system to airlines and agents for free, but when the travel agent or customer rep searches for your itinerary it would serve up hotel ads on the side and they would have to read these ads to you before proceeding.
Sabre does that now in their GUI applications. Over to the right of the blue-screen gobbledygook you'll see a little flashing reminder that so-and-so rental car firm has a hot upgrade deal in Orlando for your customers. Their technology may be antique but their willingness to sell screen space to honored pals is fully up to date.