Tangent aside, it's quite true - no one checks bags due to the fees and airlines are disinclined to enforce their rules. Last time I flew in the US I got into a near fight with a guy who was allowed to bring 3 large carry-on bags onto a fully packed flight and start to smash his bag against mine to make it fit. He did not respond to my objection well.
Now this is a case of an ass being an ass, true, but he refused to allow the attendant to check his bag because of "fees"; whether or not you pay them at that point is kind of irrelevant as it's the fear of the fees that get people riled up. Personally I'd be fine with the fees, but the airlines also mistake customer service with just not enforcing their own rules. So people who do pay fees or pack more appropriately end up getting screwed and those who try to skirt the fees bother the rest, and the airlines don't seem to care either way.
I don't know what the difference is with US domestic and EU International, but during my time abroad, I've never had this issue, but I've also noticed that the attendants for non-US airlines have no problem enforcing the rules.
So from my experience, it's just a matter of US Domestic flights trying to do as little as possible to be a service provider while charging the same as any other airline normally would. Even Aeroflot is better than US domestics.