This is categorically wrong when applied to quality steel steerer tubes, which are normally butted with a taper from the thin, unbutted section of the tube to the thick butted end of the tube which is the end brazed into the fork crown. If a steerer was cut for a small frame, it is possible that the taper to the butt or the butt itself could restrict the insertion of the quill. Spiral splines in the tube are just another way of butting the end and are also tapered from the thin, unbutted section to the thickest part of the spline/butt.