I usually fly with an American style (big) carry-on. I have found that on KLM and Air France intercontinental flights even if I board late on a sold out flight there is room for my bag. This contrasts with US domestic flights where if one doesn't board early there is no more overhead space remaining.

I have always attributed this difference to the fact that on KLM/AF intercontinental flights everyone gets at least one free checked bag, while on domestic US flights most non-elites do not.

However, KLM/AF is now implementing "Light" fares, where elites no longer will have a free checked bag. My guess is that more passengers will now attempt to bring on steamer trunk size carry-on to avoid the checked luggage fee.