The 80 is not rated for the weight in that US. Meaning, it is illegal to use it to tow that much weight.
It's not a lawsuit, it's the law.. Like speeding or running a stop sign.
First off, it's not just a lawsuit, it's a long discussion with Johnny law about why you exceeded the vehicles tow rating.
Sorry, but this is flat out incorrect.
First off, there is very little in the way of Federal law regulating this. DOT has some very basic regulations regarding towing, but most of it deals with lighting and some basic safety requirements (chains, breakaway systems, etc). The vast majority of the regulations are
state, not Federal. So saying "the 80 is not rated for the weight in that [sic] US" is not correct, because there are no Federal weight regulations that I'm able to find.
Now states have quite a few regulations on weights...but the ones that I'm most familiar with (Oregon primarily) we'll quite literally never hit those limits. They really only apply to big rigs, not personal vehicles. We're talking about limits like 34,000 for two axles (even I'm not going to suggest that an 80 can tow that!

). And that's the
smallest limit.
Now other states DO have some weight rating limits that a non-commercial vehicle would fall under, but Oregon (and many others) do not.
How Oregon limits weight is actually quite reasonable (more so than a some other states laws I've looked at), they do so by looking at the
performance of the vehicle. Basically if you can safely stop it, you can tow it.
To quote from Oregon DMV's page:
4) Do I have to have brakes on my trailer?
Answer: Oregon law requires that any vehicle or combination of vehicles weighing less than 8,000 pounds must be able to stop within a travel lane in 25 feet from 20 miles per hour. If the vehicle or combination of vehicles weighs over 8,000 pounds, the vehicle must be able to stop within a travel lane in 35 feet from 20 miles per hour. Check your owner's manual of the tow vehicle to see what the manufacturer recommends. Most manufacturers recommend trailer brakes if the trailer and load weigh 1,000 pounds or more. (ORS 815.125)
Note that the last two sentences are a
recommendation, not a regulation (it's not found in ORS 815 or anywhere else that I can find).
For most states, weight is unlikely to be the limitation that you hit legally. There are many other ones you may hit, and what's legal in one state very well may not be legal in another.
Here's a link to a page that has a massive amount of towing regulations on it, it's a great resource if you're planning on towing (and especially crossing state lines). There's a lot of stuff on there that I wasn't aware of that was regulated, and areas where you're fare more likely to get into trouble than weight limits.
http://www.towingworld.com/articles/TowingLaws.htm
Consider this, how many big rig weigh stations are you going to be driving by on your trip? Highway patrol tends to take weight ratings seriously and you plugging along at 50-55 on a 70 mph highway (and slowing down for corners) will stick out like a sore thumb...
You do not have to get in an accident to have your trip cancelled rapidly and expensively by a man with a big hat and gun...
Around here you wouldn't. Highway patrol takes speed limits seriously, and even in Cali where the speed limit is 70 MPH (all 65 in Oregon), the towing speed limit is still 55.
So plugging along at 50-55 would get you a nod from the State/County/City law enforcement, not a ticket.
FWIW out of the 64 listed (that includes Canada) only 15 have weight regulations that we'd fall under, even towing 7,700 lbs. (The rest either have no regulations or regulations that would only apply to commercial rigs.)
They are:
Alberta, Yukon, Manitoba, Ouebec, British Columbia, Connecticut, Arizona, Kentucky, Lousiana, Nebraska, North Dakota, Utah, California, New Mexico, Flordia
That's only 10 out of 50 US States, so I guess your blanket statements are correct 1/5th of the time.
Oh, and to boot all those mentioned above (except Yukon) have reciprocity, so if you can prove you're following
your state laws, you're still legal, even if you're over the limits for that state.
TL;DR: Know your state (and any states you plan on passing through) laws before you try and tow.