Most will still serve food, especially on the longer and international flights. You musta been traveling on Southwest Airlines. It's like a cattle call...
I flew US-Air twice this year, and ATA once. We don't have Southwest out of Pittsburgh, I don't think.
I believe USAir had food for purchase, but it was expensive and nasty-looking. ATA is about one step up from Southwest - you at least have assigned seats. But they play country music while you're on the tarmac. When we were delayed for two hours out of Chicago, I nearly went insane.