Here are some threads from a couple of years ago where the "JW" distinction was discussed, What's with the JW Marriott Properties?? and What, specifically, is the difference between a "JW" and a regular Marriott?. I'm not sure that anything truly definitive was ever really found in those threads, but they both have some good info in them.

Also, if you check out Marriott's website here, Marriott seems to be "marketing" the JW brand as less of a business hotel and more of a luxery hotel. This matches some of what was brought out here and in the other threads.