I wouldn't jump to that conclusion. If you look closely at the spreadsheet (provided by a trailer builder), you can see that there are weight restrictions listed that lead into supplemental braking requirements, etc. which makes me believe this list is for all trailers.

I would think that unless you're involved in a collision, or you come across a really bored trooper, you're probably OK. Although, I do recall a story about a guy taking a Hobie 21 through the toll booth in NH and getting an earful from the toll collector a few years back (he got tired of telescoping in the crossbars)...

There are other laws that aren't listed here. Some states require additional signals if the load exceeds a certain distance from the trailer (or car I suppose) lights. So many feet requires a red flag, so many more feet require additional lights. You can see where this applies to our masts, especially when towing behind an RV.

But, to answer the original question, to mass market cats, manufacturers are wise to stay within the highway limits. People are lazy enough as it is, if they have to jump through hoops to make their boat/trailer legal, that's one more excuse to buy something else.

Mike