Nigel,
What is really impressive is how good the figures are without new carriers and masses of new routes. It means the broad spread of carriers that BHX has - and it has a broader spread than most UK airports outside London - are enjoying success, and hopefully making good money, which is what their businesses are supposed to be all about.
I really don't see the range of airlines that BHX has as a worry. I would worry more if another "cheap" carrier parachuted half a dozen extra aircraft in and flooded the market.
Over time those existing carriers will grow organically - perhaps AI going daily; Emirates increasing capacity - perhaps a third service, increased capacity from the likes of LH / TK / KL / AF and new routes from the two biggest based carriers. I must admit I am concerned how long a single daily Newark can survive - but as long as it remains profitable enough, I guess it will hang on.