The contract between the designer and the manufacturer spells out what is printed on the selvedge. So it's really a restriction on the manufacturer as to what markets the manufacturer can sell into.
The ones that bug me are the ones that say "Use beyond individual consumption requires a license." That's also dictated by the designer/licensor, but is very misleading to the end consumer, upon whom there is actually no restriction as to how they can use it, up to and including making it up and selling it publicly.
My point is that printing something on the selvage has no legal standing whatsoever, so why put it there when it will only annoy the end user?