I've been reading about ST versus LT tires lately. My "research" is coming from sources like Les Schwab, Tire Rack, American Tire Company, Big O Tires, Discount Tire, etc.
They state that ST tires are built differently than LT tires: different/tougher materials to resist weathering and cracking due to ozone, stiffer sidewalls, thicker polyester cording, steel cords with higher tensile strength ... all to meet the higher load requirements and demands of trailering.
Genuinely no offense to anyone, but why are these sources not reliable? Are they not experts?
On a side note, I have seen that there are a couple of ST models (Goodyear Marathon, and another I can't remember) that are rated up to 75 MPH with proper inflation.