I'm sure that the food or service is not intentionally any worse than at other resorts; in fact I believe it is as good or better and many threads here would support that.
There are two factors that come to mind. One is that at the Polynesian, non-suite concierge rooms are the same as standard rooms (aside from having a free refrigerator). Another is that half of the non-suite concierge rooms (in the Hawaii building) have a standard (garden) view, and these are priced considerably cheaper than the lagoon view concierge rooms, which ARE priced about the same as concierge at other resorts.