People blood get accustomed to certain temperatures in the area that they live in. If you took Tucson students and put them in England during the summer when it is hot they probably wouldn't think it was hot but some would probably would consider England cold from what they are use to.
In the UK hardly anyone has air conditioners and even fans, it is a great place for American to visit during the summer.
I'm pretty sure those schools in the UK with out air condition or fans get pretty hot during summer.
People in Florida break out the sweaters when it gets down to 70. People in Minnesota break out the shorts and t-shirts when it gets above freezing in winter. Hot or cold is all relative.