Cars yes, but with diesel over $5.00+/gallon there are very few trucking companies that will allow their drivers to go over 65 mph. It's simply too expensive.
The ones you see driving around at 70+mph are usually owner-operators who don't have their trucks governed.
Anecdotally, as someone with a lot personal experience driving an RV down the road capped at 65mph, I get passed all the time by big trucks. I do see plenty that are likely governed at 65 though.
Plenty are in the US. A lot of people from other countries don't appreciate just how much open space there is to cover here.