You make an incorrect assumption.
Yes, I carry my laptop...and only my laptop on board.
I always check any luggage regardless of size because I don't want the hassle and I leave plenty of time to pick it up.
I have actually had an attendant suggest I have my computer checked because there wasn't enough room in the bins due to the very, very many pieces of oversized luggage stuffed up there. I made it very clear that one of those foot lockers will get checked before my computer gets tossed on the conveyor belt. That may be uppity, but so be it.
And because I travel so much I frequently find myself in first class. As you are aware, 1st class gets seated first so I get to "people watch" as people board. More than once I have observed someone put their luggage in a bin over my head and continue onto coach. Guess what? I grab their bag and return it to them in their seat!
And before you completely label me....I'm one of those guys who gives up my 1st class seat to a man/woman in uniform, although I will admit only for flights of three hours or less.
AAAAAND if they charged me for my weight....I'd have to take the bus.