The only reason I pick on this thread is because most of it is pure speculation. I got to wonder,,, is your inrush more than mine, is your service more severe or heavy duty? I have put the 40 centers on the welding bench where they saw 1000's of cycles, on chop saw with 40A inrush and near 30 load, on table saw and on 1 hp motor to the paint fan and another 1000 besides the hundreds I own for customer types.
Why aint they broke? This assumption, along with many of the things I thought about all this have changed over the years as I listened to the same logic when I started, as time went and I got actual experience found out all the hearsay wasn't so accurate and "someone told me" was not always a great authority on all of it.
I would have quit using 9it had it not performed and I have a pretty good sized pool under varying circumstances to measure it against. A little like the wrench and socket debate. The guy who changes oil on a 16 fusion and works on his hobby Jeep cant compare to a career in agriculture and oil field as to the real longevity of tools, not always my own experience but seeing others.
A guy on a service truck in a particular trade may see a few more, he may also have personal preference or even jump to some of the same conclusion but the failure/problem rate of the economical recept is pretty low, this is something the mfg doesn't want warranty or recall on in a big way.
They also in some cases put the exact same **** in the box with a different style or even label,,, hence the various warranty on the water heaters. Does anyone want to track all the little **** which costs a few cents to shave margins when several dollars are made for slapping a different sticker on?
Do we figure they track all the steel in a napa wrench vs a Cman, the various tips on screwdrivers or change the contact metal in every recept? They don't have a better mounting screw on a 3$ one than they do 50 center.
the 15 and the 20 use the same metal. Its pretty much purely speculation that one is better than the other.