It's more likely the 8% spandex. 100% Nylon garments are nearly bulletproof. I have a couple pairs of nylon shorts and not much else to wear. They get a LOT of wear and machine washing on high. They're nicer than the day I got them because they're finally starting to soften a little bit...

Spandex blends always wear out, though. They get baggy and warped, and the rubber starts pilling out. It's nasty.