Edit: I think a lot of people just naturally don't pay much attention to what they're doing to their cables. I used to work at a company where I was pretty much the only one whose MBP power cable wasn't visibly fraying at the ends, and I'm still using the same one 5 years later.
I like to open the one on my building, and have a peek to see if there's something interesting. I like repairing (often just resetting) discarded electronics and donating them to people who need them.
Anyway, I find loads of broken Apple cables, but very few plain USB cables.
I am guessing usage patterns will explain the difference.
Not using the phone while charging negates this, as does having the cable flat on a table when using the macbook (as opposed to using and charging with the macbook on your lap, where the cable rops down immediately).
This, combined with poor quality products explains the difference in my opinion.
The only cable that frayed on me was a MagSafe 2, next to the computer connector. The cable is ridiculously thin. It was the adapter for my 15 MBP. In comparison, I'm still using the original adapter of my 2008 MBP and apart from being scratched and dirty, it's still as good as new, cable and all.
What I think happens often is that the cable will be under some kind of rotational stress. I've noticed I have a tendency to always turn the phone the same way, so the cable has a tendency to turn around its axis. It's something I see especially often on corded office phones. Also, cables are often at very tight angles close to the connector, so there beign next to no relief ends up tearing the housing.
I've also seen many people pull on the cable instead of the connector to uplug it. That can't be to good for longevity either.
That said, I travel plenty, and I shove cables into my bag like anyone else. I can't think of a single cable for a single product (Apple or non-Apple) that I've destroyed. Some peoples' cables look like they get slammed in a car door twice a day every day.
this is me and i replace these regularly
I'm pretty sure it's from heat damage from the power. Not mechanical strain. The heat slowly weakens the rubber material to the point of failure.