While I've never seen the PVC jacket on CAT3 or CAT5 cable break, I've seen it on rubber and PVC covered audio cables in nightclubs dry out and break after a few years. I suspect the nicotine from all the cigarette smoke contributed to that.
Other than very, very, very old cable (and CAT5 hasn't been around that many decades) or cable left in the sun, I can't imagine it breaking unless you have some sort of extreme mechanical stress...in which case solid conductor cable won't last at all.
With that said, yes...some CAT5 does appear to have a thicker PVC covering, but its not predictable when you'll find it. For example I bought six boxes of grey PVC made by General Cable from Home Depot tree yeas ago and one box of cable had a jacket that was twice as thick as the other boxes.
On a side note about sunlight damage...white nylon wire ties last one summer in the hot Texas sun and shatter when the next summer comes along. Black one are more resistant, but they too will break after several years. Same with non-outdoor rated PVC covered cables.
With high heels on. If woman weighs 120 pounds and stands on one high heel with a quarter inch square area, thats 480 pounds per square inch...and thats not counting the increased impact pressure of a foot step.