Just be respectfull as much as you can even though you just flew multiple hours and it's 1am and all you want is a clean shower and a fine meal just because Argentina lost another final... ahh sorry bad memories
In the old days they were lazy and handed out Visa Waiver forms to everyone on the plane. Perhaps they've stopped doing that. The Visa Waiver form is the famous "are you a terrorist?" Q+A forum. You don't have to fill that out if you're a citizen because entering the USA as a citizen never requires a visa. Theoretically if you have a visa (are a citizen of a non-visa waiver country) someone already signed for you and investigated such that you're not a terrorist and filling out a visa waiver would be pretty pointless if you require and have a visa.
Immigration officials seem to delight in pulling peoples chains, and you have nothing more interesting to do while waiting in line, so local variation and variation over time is highly likely.
The agents are usually polite and friendly. But they aren't always, and that can be intimidating and infuriating if you're a US citizen who's simply returning home from a trip.