True the JB3 is not in production any more, but they still are fairly easily found if you want one. The D7, D8, D100, and M1 are not in production anymore. Even the DA-P1 might now be out of production. But people still talk about using DAT decks as their recorder of choice.
That said, some folks think that the JB3 is too unreliable to be trusted as a field recorder (rightly or wrongly). So there might be some benefit in a PMD660 even if it only does 16/44 or 48. Maybe PMD660 vs JB3 is more like DA-P1 vs D8 -- for our purposes they might only be doing the same thing, but one might be more reliable. Of course, I have no idea if the 660 is more reliable, but at least it was built to be a portable field recorder.