I chatted with a couple of MS customer reps. In essence, what they said was that their clientele had always been the more traditional backpackers. While the Ghost sold really well, they also got a lot of warranty returns all across the entire "Mountainlight" line (i.e. Ghost as well as Auspex, Phantom, etc.) from users buying light weight packs to haul the same heavy gear! This prompted them to "return to their roots" so to speak in the beginning of 2006. Looking at Mountainsmith's current website really bears this out.
Interestingly, as a light weight hiker, I find the material used in the Ghost quite robust actually! For pack weight of 25lbs or less, I wouldn't hesitate to buy this pack again (actually, I would, because I've already got two of them, and even after three years of use, I haven't even begun to wear one out yet).