I think some people at Apple are sensible enough to realise that many companies will be staying with OS 9 until OS X has proven itself and can run essential app's natively (say at least another year).And thus OS 9 support will continue a while.
I don't think Apple are quite killing OS 9 yet, and 9.2.1 seems fine on my no longer cutting-edge G4/400, and although this update is mainly for improvements in using OS 9 within OS X, and thus recommended only for OS X-ready machines, you can install it on "unsupported" Mac's. Details at www.xlr8yourmac.com
. Benefits unknown.
I too was deeply afraid of this alien OS X/Aqua thingy taking the life-blood from the traditional Mac OS, but recent (5G24) builds of OS X have greatly appeased me. I'd take another look at OS X when 10.1 is released.