Thickness counts for durability, and you have choices. I'm not sure what durability is like for cotton blends (it's rarely more than 3-4% synthetic). I have doubts that mass-produced denim of similar weight is significantly more or less durable than denim from traditional looms. The only differences I can think of that would impact this would be staple length and chemicals used in processing. Pre-faded, bleached, or distressed denim will obviously be less durable.

20 years sounds high to me. I have jeans less than a year old already showing crotch wear. Granted, this is expected, and it can be repaired before it's an issue.