I don't know how I never noticed this until now, and I could swear that this was never a problem before logic 8, but after further investigation I've discovered that this problem apparently has always been present, because I booted off one of my ext firewire drives which is an image of my HD from 5 months ago and I was able to replicate the problem .Ok here's the issue:
Even with the exs set to 64 note polyphony I'm hearing the first notes played dropping out when I play long sustaining piano runs. I had my friend who's also running logic 8 try this at home and it did the same for him, so I know it's not just my setup. If any of you want to try this, simply load the steinway piano into the exs sampler, keep your foot on the sustain pedal through the entire test, and hit any low key, then play a bunch of notes up high and release your hands from the keyboard, then just listen to the sustaining notes, you will hear notes start dropping off, most likely starting with the low notes you hit first. I have tested this with all different pianos and it does the same with all, I haven't tested other sounds, but I would imagine it would do the same. I first put this under MainStage, but it does the same thing if I load the sound into Logic 8, so I figured I'd put it here.