Adioso began as a single source for price search to low cost carriers and the low cost carriers are not in the GDS because they won't pay the prices.So I presume they scrape (spider at regular intervals) the low cost carrier prices from the airline websites but possibly they have api direct links. Tom could tell us. (Tom I really want an in depth post on wingtip!) But to do fast real time search for hundreds of airlines you need more than a fast schedule (time dependent graph) you also need the complex fare rules worked out and programmed. All of that data is available but costs. The last bit is you then need to check availability via wherever you can book the ticket (GDS or direct to airline) and cache it for speed. I think that the fact that Tom links to Vayant's price cacheing api it is an admission that it isn't raw data that's lacking it's a higher level api where fares and availability are already worked out. Because seriously to do that yourself is a huge time & engineering challenge. It took ITA years. Adioso have the fast Graph and can get the schedule data. Vayant is offering an off the shelf solution to do fares and availability. Could work.

Right, makes a bit more sense now. Thanks for the thourough explanation. Also, I would too be interested in a post which gives more insight into Wingtip as it sounds quite interesting.