Family flyer: you're quite right (although some airline boards seem more critical than others -- and I do remember that critical also means evaluative, not just negatively so.)

We're left with the possibility that something about Marriott frequenters makes them less likely to (a) find & enjoy FT or (b) use it as much once found.

I'd guess (b). I can't find a thread here on the M-series discounts from the newsletter, for example, or the $109 rate later this winter at San Diego Marina (noteworthy, I suppose, but it never occurred to me to tell other folks). Also, there is no official Marriott presence here, as there has been on Hilton & Starwood, to answer questions and deal with problems; that might stimulate more postings there. FWIW.