Its a calculation issue, need your product id to make the correct memory calculation
Microsoft should just report the "installed memory" capacity. Adding the "usable" amount just confuses people since the usable amount will almost never equal the installed amount.
Here is a link with the explanation.
http://support.microsoft.com/kb/978610
Surely you don't think you'd actually NOTICE the extra 100mb of memory? :\
This is already 2x-4x as much RAM as you're probably ever going to utilize anyway.