I have used tubular webbing for perimeter line with mixed success. The most readily available tubular 1" webbing is nylon which exhibits noticeable shrink and stretch which is not ideal for chicken lines. The commercial flip lines I use are webbing and have worked fine over the years.
I wouldn't agree that "there are not many very good reasons to use rope" for the stated applications. I for one have a variety of knots that I can use with a rope that are less than ideal for tubular webbing, like a taut line hitch for an anchor rope at camp which is the handiest I know for adjusting tension for tidal fluctuations. As well, the stern and bow lines can serve double duty for rescue situations in which the difference in breaking strength matters. Rope tends to work better in rescue situations that require mechanical advantage that use prusiks, or comparable knots, pulleys. Unlike webbing, rope has a protective sheath over the load bearing strands which increases longevity (abrasion, UV, etc).
And as I understand it the concern of D-Ring strength is of limited use in rescue situations as its best to tie off to the frame if possible. D-rings are not to be pulled on outward in that fashion and by attaching to the frame you are essentially using multiple anchors. I would also wager you gain some strength from the surface tension of the polypro straps on the rubber raft going from the D-Rings themselves (assuming it behaves similarly to running a climbing anchor over the surface of rock but I could be wrong).
Both have their strengths and weaknesses and there are definitely many circumstances in which either will serve the duty. That said, I won't be giving up rope for a bow and stern line anytime soon.