Outside programs that specifically force the max amount of ram to be used, the 6 and 8GB ram works very well on the MBP. I use it mostly for virtual machine work. I can run several VMs at once without lag anymore because the system has more then 4GB of ram to work with. That is what I usually use my laptop for and I found success in my trials. It is not just a "About Mac" trigger. There has been several screenshots that shows it can use that much ram, however, the method being used might not be what you're looking for.
Edit: I ran your piggy. I ran 5 Windows, with VMWare Fusion running Vista at 1GB dedicated in the background. 0 CPU usage for your piggy once its loaded. However, the system does not want to hold the memory in the actual, it keeps wanting to dump it into swap. If you can write a program that works in 64-bit windows, it would really prove if this is a software or hardware fault.