I had read that also and believed it. But I think the threads are always cut. It they were rolled the OD of the threads would be bigger that the OD of the steer tube since material is pushed out. In anycase I talked to the Kogswell guy (I wanted a fork from them) and they could cut threads on a naked steer tube. Don't know if it is heat threaded though.

So it should be fine to thread it then cut it at length. The tube is indeed weaker where the threads are, but it's ok as long as the stem wedge doesn't push against it, i.e if the threads aren't too long. It's silly nowadays they sell threaded forks with a long steer tube threaded almost all the way so it can be used on any frame. And I've seen pictures of such forks destroyed because of the stem. Don't buy them if you have a large frame!