The reason for the difference isn't quality driven, as Bespoken said. It's an aesthetic choice. The tighter heel makes for a dressier product. On 270 degree welted shoes, the heel zone of the sole is nailed on. After the the leather upper is lasted, a heel seat is nailed on, with the nails being driven up through the bottom and clinching into the leather insole. Lasts have a steel plate on the bottom, which causes the nails to bend and clinch the leather when they strike the plate. The sole is then nailed in the heel area in the same way, before the actual heel stack is nailed on. The nails are covered up with the leather cushioned sock liner that you see in other Goodyear-welted shoes. Contrary to popular belief, that sock liner's 1st intention isn't to pass on comfort to the wearer. It is to cover up the nails that are holding on the rear of the sole and heel. AE doesn't make their shoes this way, so those sock liners aren't "needed."
It is cheaper, easier, and more streamlined to manufacture 360 degree welts. That's the reason that AE sticks to that design. It isn't a cheaper shoe from a shoe quality standpoint. It's just different. 360 degree welts don't need shanks, and they don't need as many nails. As mentioned above, they also don't need sock-liners if the sole isn't nailed on at the heel. They also save a couple of steps in the manufacturing process, which eliminates the need for people to perform those steps. Those savings are passed on to the customer, and is one of the reasons AE is a more affordable shoe. Of course, that's at the expense of a more refined looking shoe on some models which may actually be more aesthetically pleasing with a 270 welt.
All companies that do Goodyear-welting (with the exception of AE) alternate between the two methods depending upon what is most appropriate for the style of shoe and its intended function and level of formality. Traditionally, country or casual styles may be 360, while dressier styles are 270. AE's company model just disregards these traditions in favor of streamlining their manufacturing.
I love your posts. So much good information in there!