I've seen the "machine sewing" of the steeks on a video on KDTV. But I've also seen the carefullly "hand stitching" the steek, too.
I took a COLORWORK class a few years ago. Sandy Blue, from Rowan, excels in Fair Isle. She taught us to hand stitch a protective line inside the steek. If you carefully take small stitches, it will protect your knitting.
Besides, as Sandy taught us...knitting doesn't ravel sideways. The stitching step is taken just as a precaution, and to make you feel better about the CUTTING.
IMHO, you don't need to run out and buy a sewing machine for the sake of protecting the steek issue.
But here is a tutorial
that expands on all sorts of Fair Isle steeking...including crochet, machine, hand sewing.