To be fair to BA, their argument/theory is presumably that the First pre-flight dining (whether it is called that (ORD, PHL etc.) or "Concorde Dining") is not a lounge but just an "on the ground" meal service from the First cabin...
By the same token, BAEC Silver (and Gold/GGL) can access the Club lounge at JFK, but only Club World passengers have access to the Club World pre-flight dining for the sleeper services.
I agree it's a somewhat bizarre distinction and calling the First pre-flight dining "Concorde" at some outstations clearly confuses the issue...and I agree that for the sake of an additional 5-10 visits a week it hardly seems worth penny-pinching your best customers - but it's not entirely without precedent.