We tow a rear kitchen (pronounced: "heavy behind the axles") with a SRW, short bed F350. Even when the trailer is fully-loaded, it's about 7,900-8,100 lbs, so we're well within the capacity of the truck. However, because of the trailer's layout, we feel completely comfortable with the power and heft of the TV with a trailer like this one.
Aside from any liability issues that may come up if a problem occurs, I can't imagine that if someone has a towing capacity of say 7,500 lbs, that everything would be brilliant up to that, and it'll all instantly go to hell at 7,501 lbs. Having said that, I like having a healthy buffer between towing capacity and towing reality. :)