It might be a missconception but then it's a very spread one. Since I started with neps I've been reading and watching about "the trio" (Villosa, Eddy and Macrophylla) and how they all are pure UHL. Where that info comes from I have no idea but it might be worth to correct.
Where did you get the information?
I grow N. macrophylla and N. edwardsiana in my greenhouse alongside all the others, and summer temps this year hit 82-87F every day. (Bear in mind that nights in my region drop into the 50s without fail, and humidity is very carefully maintained in the greenhouse at all times. These factors play a significant role in how well or how poorly highland plants tolerate warm days) These two species are thriving in my care. So much for the "ultra highland" myth.