Because for OSX you should have at least 256MB RAM if not 512MB, plus a decent speed CPU? My 450Mhz G4 with 1GB of RAM is right on the outer limit of acceptable performance.
You can put a gig of memory in a Blue Bondi
What problems would you expect with a Mac under 450 mhz?
I have a 400 mHz G3 iMac, with 640 mB sdram, and OS 10.3.9, recently installed.