Lowfaresbuster:
I don't think you're comparing apples with apples.
Unless I'm mistaken, the UK numbers you quote are city populations only, which frankly are pretty meaningless - what's much more important is the number of people within say 60 or 90 minutes journey time of the airport, irrespective of whether they're living inside a given city boundary.
I don't have detailed catchment numbers for all the airports you've cited, but - to take BRS as an example - Avon, Gloucestershire and North Somerset (a reasonable catchment for BRS, I think) is about 1.5 m people I believe. Hopefully a knowledgeable soul like Merchant Venturer can help us out.
I appreciate the (well-founded) desire to see more services out of ORK, but creative accounting with the catchment numbers to overegg the case doesn't really serve anyone.
C.