There is definitely a feeling that you've entered a Greyhound bus station when you enter the land of a lot of express carriers. This is true of 35A at DCA, and was true of the "E" gates at PIT. And the experience is not limited to just US.

When I was in college in the early/mid 1990s, I got to and from school via RDU when AA had its operation there. Anyone remember infamous Gate C16? The downstairs seating area with old worn seats and carpeting where Leroy, Kenny, Wilma, and Cletus would patiently wait to board their J31s, SF340s, and Shorts 360s to fly to LYH, CHO, ROA, ILM, and any number of little cities...