I've been shopping around for a lawn tractor for about a year now and have driven a bunch and have done a lot of research. I'm not an expert but I have formed some opinions. The L series JDs are a small notch better than the Craftsmans and I don't consider them "real JDs" (just my opinion). You need to get at least an X series to get a real JD. The quality difference is very evident and the fact that a you get real engine (Kawasaki vs B&S or Kohler Courage). The engine in the tractor tells you a lot about how well it's built. It's a quick litmus test for quality (not perfect...but pretty good). I always though I would spend $1500 on a lawn tractor but now it looks like I'll spend twice that to get one that would last.
Common marketing gimmick...put a popular engine on a bunch of crap parts, and everyone thinks it's the greatest thing since sliced bread. Ain't nothing wrong with a B&S engine, most people won't know the difference in the end anyways. Proper maintenance is the key to longevity, not a gimmicky engine.