You actually noticed a RAM consumption difference of 10 MB? On a modern computer? Wow! 😱
I haven't noticed...and both of my Macs are on 10.4.5 now, so I can't test for you. Sorry. 🙁
But right at this moment, here is what I see in 10.4.5:
iMac G5 / 2.0 GHz / 1.5GB RAM: Finder has three threads and 32.5MB real memory and 252.5MB VM.
iBook G4 / 800 MHz / 640MB RAM: Four threads, 14MB real memory, 194.5MB VM.
So there's a lot of variability... are you sure you're seeing a change due to 10.4.5 and not variability?