The rating of semi trucks at 80k lbs has more to do with the weight distribution over the road for an 18-wheeler than about the limitations on the powerplant and brakes. If you take a look at various low loaders and other oversize/overweight load setups, the biggest change is adding more axles (often tag axles). Because of the length that this results in you will often get into situations where various escort cars are required.
That said, I do agree that the bigger concern in the case of 1/2-ton trucks is brakes and suspension more than anything. However both those items on a modern 1/2-ton truck are way, way better than what existed 20 years ago. When
@jesse bought my boat he had a late 90s 1/2-ton Chevy Silverado. I told him that he would end up towing with it once and the first time he hit the brakes while in Lincoln and finally came to a stop somewhere around Denver he'd decide he'd want an upgrade. Sure enough, a few months later his new F-150 ended up in his driveway and it tows the thing much better. The boat with trailer is something around 7k lbs so it's a good fit.
Towing my 25' trailer with the bulldozer on it (combined weight of something around 14k lbs) I am happy using my 1-ton Ram. The fact that it has a diesel is nice engine wise (especially because of the built-in Jake brake) but the suspension and brakes really feel at home with that kind of weight.