While key velocity triggers the volume played, there are other factors such as after touch, and SA voice effect triggers that apply to Yamaha's key system. It's a fairly complex system, and I for one, don't have the answers for why any manufacturer uses the systems they use.
Not only that Gary, but you, Joe and Donny seem to be very comfortable with the PSR action, and I suspect if it was as bad as being implied, I doubt very much if you pros would put up with it.
Considering that the PSR has 61 keys, I doubt very much if it's biggest and most persistant critics would even purchase one.
I must say, I found the PSR keys very pleasant to play, and was seriously considering an S910 (or maybe S950) before I got a break and was able to afford the Tyros4.
The PSR has a fine velocity response, and yes, the throw is shallower than some others, but the clincher for me was that you could turn the volume up to 3/4, pick a piano sound, press a key slowly enough, and actually get no sound...the same as an acoustic piano key.
Plus, as you have learned with your 3K's...it's pretty darn reliable as well.
Also, you, Joe and Donny all have different playing styles, yet it works well for all three of you.
Not bad, eh?