I have trouble embracing the idea that a manufacturer would want to use a rolling process for putting threads on a steer tube, given that the tolerances of 1" tubing are what they are(?), and with the threads and wall thickness being so shallow and thin. A variation of thread depth might result from the combined tolerances of wall thickness and roundness unless the tubing was of a very high-tolerance that would be expected to increase cost.
I could almost imagine that a needed mandrel might flex enough to require something akin to a single-point rolling operation, which I've never heard of, since a substantial length of threading is often applied, or more likely that the ID of the tube might end up out of spec (oversized) from the rolling operation.

I can't recall having ever seen a steerer that appeared to have rolled threads, but have noticed that new ones always look to have cut threads.
And, if any maker did use rolled threads on a steerer, you would think that they would tout this in their marketing, as it would likely have been costly to accomplish. But then, they would have to be able to say that they also rolled or formed the flat or groove, so as to be seen as consistent in whatever argument for rolled threads that they put forth.
So, in the well-remembered words of my enthusiastic high school trigonometry instructor Mr. Kutnohorsky (or "Cut", as the hipsters referred to him), when referring to the use of any less-than-simplest approach to solving trig problems, "It's a nightmare".