You could call it uality control, I call it manufacturing variances that are allowed. Anyone over the age of 30 has bought enough jeans in their lifetime (and I learned this with Levis by the time I was 20) to know that you take a stack of whatever size you think you are into the dressing room, assess each pair, and buy the ones that fit you correctly (if any). Levis easily change pant-leg width, inseam, and wait by as much as an inch from pair to pair (rare to be that much, but I've seen it), so they just aren't something you buy off of the rack without trying them on. But then Levis are more mass-produced than something like motorcycling jeans that have Kevlar in them. The variances will most likely be wider on high-spped production runs with pants like Levis comapred to pants that have Kevlar that is most likely hand-cut. Now I'm not saying that riding jeans don't have variances, as really everything does in manufacturing, but I would believe that riding pants are more true to the size the maker intended (which isn't to say one maker's 32" inseam is the same as someone else's, or even the same across same makers' different product lines).