The point is that heating them up doesn't ruin anything. at least not to the temps involved for any of these materials. A lot of people are getting them red hot or they just don't know what red hot is. There was a thread a while back about a video of a Japanese frame builder who was brazing his tubes, which is a different mater. It drew a fair amount of coment until some old pros jumped in and said that was how hot it should be. You should always use the least heat you can, but there are misconceptions across the board about how much that is or what it is doing to the tubes. If nothing else, cooler is often less clean-up.