G-KEST,
You're right that the PFA has a wider range of "conventional" types, but the BMAA has a very wide range of aircraft under it's wing now. Also, virtually all microlights were homebuilt until about 20 odd years ago, so they have been looking after homebuilts almost since the day they were first approved. The number of homebuilts that the BMAA is looking after is roughly doubling every year (I think about 60 or so have been signed off so far this year), and IIRC the total number of A/C they look after is now greater than that in the whole PFA fleet by a fair margin.
Of course, they probably aren't really interested in taking on heavier types, but perhaps this might change if the PFA insist on trying to take over more microlight types, who knows?
I still can't quite understand why or how the element of competition ever set in between these two associations. IIRC the PFA actively rejected the idea of having anything to do with microlights at the time that the BMAA was formed. Someone once told me that the formation of the BMAA came about as a pretty direct result of the PFAs action, so it seems odd that rumours of the PFA extending their exposition to take on more microlight work from the BMAA seem to now be doing the rounds.