Nah, that’s really a holdover from the period when poly was just taking over and the strings were considerably thinner and the quality much lower (AND the wood/axles in the fixies available was way rougher). Gotta remember that before 2007 or so, full poly was junk with most players using slick (50/50) for modern 1a. If you want to see a string melt, grab a brand new russell and some ~2005 shiny white poly and try a couple Warp Drives (ideally near some windows).
With the standards/thickness of current poly string and the smoothness of modern wood, you’re just as safe throwing cotton as poly. I do prefer the feel of cotton with wood, but just because it’s what I’m used to.