How many controllers actually know what all those different letters mean on the flight plan form? Not many, I would suggest. They rely on the pilot saying, "PRNAV unable" and then of course they will do what they always do and vector the aircraft to the ILS.
Many controllers have Flight Data Processing Systems which tell them the aircraft equippage for each flight. We certainly do for RVSM, 8.33, and PRNAV capability, all of which comes from the flight plan.