Senlis on 01 February 2010
from http://msdn.microsoft.com/en-us/library/aa366778(VS.85).aspx <-- note the link is to microsoft's own site admitting this
The following specifies the limits on physical memory for Windows 7.
Starter 32-bit/64-bit = 2 GB
Home Basic 64-bit = 8 GB
Home Premium 64-bit = 16 GB
Professional/Enterprise/Ultimate 64-bit = 192 GB
Of course, the limit for any 32-bit system is 4 GB (though you will probably only see about 3.5 GB of that). The exception is Windows Starter, which really screws over the customer.
I believe there is no reason for them to do this other than to get you to buy a more expensive edition of windows.
edit: I edited the table out when I realized it wouldn't fit.
