Well, I first assumed it's just for leaving live stitches but now I have to go and try it
My ribbing just has two 'walls', they are separated, not connected and knitted at the same time. and it's super easy to make. it looks puffy and doesn't stretch so much. and you can put an elastic in if you wish.
You do exactly this:
cast on even number of stitches
1r sl1, k1p1* p1.
2r sl1, k1, sl1 (keep yarn in front of the stitch) * p1.
continue for even number of rows (8-10 for elastic) or till you are bored
(does it make sense? in other words, cast on the even number of stitches. in each row, always slip the first stitch, always purl the last stitch to make the edge. make the first row as 1x1 ribbing (k1, p1). 2nd row to 10th row -- knit the knits and slip the purls.
I might come back and post my results of both methods if I manage yours
oh, and mine doesn't look like a tube, because of the edge it's 'sewn up' on the side so elastic will have to be squeezed in with a safety pin through one of the ugliest edge stitches
and it takes twice as many rows to make, so for a ribbing to look '10 stitches tall', you have to knit 20.