Nigel
I think you may be a little wide of the mark. BAA as a general rule don't "do deals" to attract airlines.
The numbers are down because RYR took their bat & ball home as a result of this policy & others are heading south of the river to LGW who (having escaped BAA control & having an ex BAA boss to boot) now will use their new found freedom to "entice" carriers in.
MAN have a much more balanced portfolio of airlines & that in part is because it serves a different region. Just like everything else in life, the fortunes of airports can go down as well as up. Ultimately STN is the fourth largest in the country, so I think there may be a few others airports who face demise before this particular goose is cooked!