Published airline fares change only a couple of times a day (10:30am, noon and 8pm), and only once a day on the weekends. Airlines (like American) are trying to push travel sites to use more dynamic pricing. The data is cached and outdated (including availability).

It doesn't take a tremendous amount of computing power -- remember that most airlines are still running ancient mainframe reservation systems.

The multiple destinations functionality was from ITA -- it's been around for years. Check out flyertalk.com for discussions -- you can input multiple layovers to have it compute cheap fares that maximize miles/segments. They keep a basic backend open at: matrix1.itasoftware.com