I'm having the same issue in Photoshop CS6 (13.0.1 x64).
I had been running my system on 16GB of RAM and recently upgraded to 32GB. My system diagnostics show 32GB of RAM actively installed and running, but when I open the system preferences in either PS or AE it shows only 16-ish available RAM. Why don't I have access to all 32GB (or close to it)?
I'm including screen shots of the Preferences Windows in both PS and AE. Any help would be much appreciated. Both applications are currently updated as of this morning.
I have answered my own question. And as embarrassing as it is. I'll leave it up in case someone else is looking for the same answer.
Windows 7 Home Premium only supports up to 16 GB of RAM. I had to buy the Professional version in order to access all 32 GB of the installed RAM.
It's a pretty silly mistake to make, but there you have it.