Another thing is that for US (and Japanese) fighters there was much more emphesis on range than most european contemporaries. Obviously the Japanese needed longer range due to the expansive Pacific, but it seems that it was the designers more than the airforces' specifications that gave the US fighters the range, or at least in many cases. I'm not sure why this is though, maybe just multipurpose designs were in mind? Even the P-51 hadn't been designed to be an escort fighter, it just turned out to fit well, and allowed very long range.
Even the P-36 had quite a longer range than contemporaries (800 mi combat), the F2A-1 was capable of nearly 1,000 mi, the F2A-2 over 1,500 mi. These were very good for the time, and for a breif period the F2A-2 had the longest range of any single seat fighter iirc. ('thll the Zero) Wildcat 800 mi clean, ~1,350 mi with droptanks. The P-40B had a ferry range of ~1,200 mi on internal fuel. The P-40E had ~1,600 mi range with a 141 US gall droptank. The early P-38 ~800 combat mi clean. (clean range setting limit to radius) The P-40N had a ferry range of ~3,000 mi with 3x drop tanks.
The P-39 was the closest thing to the compact Spitfire and 109, and even it had a bit longer combat radius. (granted the Spit could have increased fuel capacity) The Fw 190 didn't have a great clean range either (just over 500 mi) but I'd be willing to guess it could have increased fuel like the Spit could if it needed it.
Who knows what the US would have come up with for light-weight short range high performance a/c if that had been the emphesis. (the best interceptor example is the XP-72, but that was late war, and even that had good range)