Spotlight is reporting addressable memory. The two are different. see a typical explanation here: http://msdn.microsoft.com/en-us/library/aa366778%28VS.85%29.aspx
Spotlight reports addressable memory because that is the one that matters. It doesn't matter how much physical memory is installed, 32 bit windows can only address up to 4GB. Most times, the available memory is less, typically 3.5GB. on 64 bit windows there is no such limitation.
Here are two wmi commands you can run on the command line to show the difference. The first one shows kilobytes of memory available to Windows, the second one shows bytes of memory for each installed memory chip.
· wmic path Win32_OperatingSystem get TotalVisibleMemorySize
· wmic path Win32_PhysicalMemory get Capacity