just because a small airport does not have a tower does not mean it cannot be used by commercial airfare. planes takeoff from uncontrolled airports all day long. There's no reason for a huge airlines to go into a tiny airport to waste fuel and get no return passengers, it's just no economical. the reason more small airports arent used is not because atc can't keep up with the traffic, it's because there's no point in using those airports.

"Now, these are called "transponders" because they only transmit when polled by a ground station's radar sweep. And until recently, only the ground controllers received the transponder hits from the aircraft. "

Transponders are transmitting constantly whenever they are squawking and not in standby. most radar systems are comprised of two types of radar, the primary and secondary radar. the primary is what gets you the blips on the scope, and the secondary radar is what picks up transponders in the sky and associates a datatag with the blip(mode c transponders relay alt/speed info).

I think you got a bit confused here because it does not matter what position you are in in the tower, everyone can see the same thing on the scope. Until recently, only Local controllers had a use for transponders. I think you got a little mixed up here and mean to say it the other way around. You were probably thinking of ASDE/ASDE-X which is what ground controllers use to track airplanes on the ground(it uses transponders).

just to reply to: "Currently, a big plane will show up on radar as a blip. The pilot will call control, and state his/her identity and position. Controller will then make an educated guess as to which plane is which dot on the radar scope, and assign you a 4-digit "Squawk" code (Say, 1234). Pilot enters the squawk code in to his instruments, and the instruments then start broadcasting "Aircraft 1234 is at 32,000ft" on the radio. This then lets the radar display aircraft identification and altitude beside each blip. Simple, yes? Prone to human error?" only prone to pilot error right here. when an aircraft initially calls control, whether on the ground or in the air, the information is entered into STARS/ARTS and the computer generates a squawk code for that aircraft. assuming the pilot enters the code correctly and idents, the controller can then radar contact the plane verifying if the position stated is correct or not. good thing about gps is it's more accurate than radar at longer distances and will fill the gaps of cverage. the bad thing is we do not need to solely rely on a system that's airborne and can be taken out very easily, by hostility or by sheer glitches. it's a lot easier to service a radar antenna or navaid on the ground instead of something in space. we need both systems.