Threads # 213 – Add a Stretch Band to Stretch Fabrics

I am quite confused regarding an article in the Spring 2013 issue -Adding a Stretch Band to Stretch Fabrics.
I am very new to sewing with knits and stretch fabrics. There appears to be a disconnect between the stated purpose of the article of adding a stretch band for decorative impact, without compromising flexibility, and the directions that add a band, edged with fusable tape, which is then sewed on with a straight stitch and finished off with a foldover elastic.
A straight stitch on a stretch garment? Can someone give me specific examples of where this technique could be used ? Am I missing something? Looking forward to expanding my sewing knowledge.