What makes it stronger than the D44 gears; gears, axle housing, shafts...?
I shouldn't have said stronger, that's a bad word. How about "about-as-strongish"? It's got an 8 7/8 ring gear to the 44's 8 1/2. The shafts are roughly the same size, but the AMC is a 29 spline while the 44 is 30. I'd say the housings are equally as strong, but the 20 has a super badass perfectly round cover. (Feel free to correct me if I got anything wrong there.)
Either one is a good axle.