It's true, the only times I've flown as an adult in the passenger cabin is on US airlines. Just ask as you get on (the student pilot ruse is a good one) and the crews always say yes. The only times I've been denied was on a Virgin 747 with two checkpilots in the jumpseats, and an Ansett 767 where the captain was in a really foul mood. I don't know why America don't allow it, that FedEx hijacker was an employee, so was the guy who killed the crew on a USAir BAe 146. Pilots love showing off.
Another bonus that comes from sitting up there is half the time they'll being you a business class meal, cos the flight crew get one. Lufthansa are great for this, on a 55 minute flight to Hamburg recently I ate a massive spread of smoked salmon, a hot main meal and about three desserts, bathed in the comforting glow from the overhead circuit breakers on the 737-300. Plus the weather on arrival was very poor, and the pilots handled it with ease and style. What a brilliant airline.
fly Saha Air 707s daily from Tehran's downtown Mehrabad to Mashhad, Kish Island and Ahwaz