I missed your part about new content always being promised but always delivered in paid expansion packs.
This is a disturbing trend I've yet to see be bunked except in the case of Neocron. They've added TONS of stuff since release that I've seen (I don't play anymore, but I still follow it out of curiosity) and it all comes from those monthly fees. However it is the exception to the rule, and knowing SOE I doubt PS will be another exception despite my confidence in the dev. team. It'll boil down to a management decision and while I think they'll fight tooth and nail to deny it, it won't happen.