ST type tires are rated for 65 mph Max
In RV application other type tires i.e. LT & TBR type tires show 75 mph MAX in the various publications from tire companies.
Now if you think the tire companies post information simply to cause confusion or to sell more tires then that's your decision. Just be willing to accept responsibility for your actions and don't complain when your tires fail due to cumulative damage tot he structure from overload, over-speed and under-inflation along with the high lateral forces the RV manufacturers know their suspension design puts into trailer applications.
Just because you may not have been doing something tire engineers say not to do at the time of the failure doesn't mean the damage was done to the tire in the past.