My understanding was that it was less to do with numbers, and more to do with the perceived gap between the standard of bands at the top of the (old) Second section and the bottom of the Championship section. In other words, bands getting promoted from 2nd to Championship found themselves struggling too much with the sudden increase in difficulty of the test-pieces. As I understood it, the new First section was intended to provide a kind of "buffer", making the transition less severe.
I have to say, I am not convinced that it has really worked, and I don't really know why not. As far as I can see, there is still a huge gap (at least in some areas of the country) between 1st & Champ. section bands. At Egham, we find ourselves in the slightly ridiculous situation where, because of a few reasonable placings at the regionals, we are in danger of being promoted to championship section status after next years regionals if we come anywhere near the top. No-one in the band would profess that we were anywhere near Championship standard, yet the points/grading system in operation means that we could easily find ourselves competing in the Championship section in 2005!
Don't really know what the solution is.
Regards,
G.
[edit: Rats! Beaten to it]