You won't find the logic in airline pricing because it is buried deeply in the logarithms of a diabolically complex computer-controlled system. It is largely based on supply and demand, but responds to nearly-instantaneous input.
For instance, if you check prices on a flight on something like ebookers.com, don't keep going back to check it every day to see if it changes. It will. Because you're checking it. The computer recognizes your click as increased interest in that route, therefore increased demand, and it will incrementally raise the price accordingly.
I'm sure someone who wrote or controls these algorithms can be more specific, but it is so complex as to not really be worth trying to second-guess it, from what I can tell and what I do know about it.