I don't know of the exact document you are referring but Microsoft does provide some guidelines for commerce server deployments. There is no convenient rule that says X number of users will need Y number of Commerce Server licenses. According to Microsoft:
" One site may support 1,000 users, while another site installed on an identical platform may support only 200 users because of differences in user behavior." - from this page about Capacity Planning: http://msdn.microsoft.com/en-us/library/ms962464.aspx
This page (http://msdn.microsoft.com/en-us/library/ms961993.aspx) gives the requirements for a "typical" installation, whatever that is. You can see from the specs the page is from a time long ago.
More recently MS released two guides, one for a base deployment and one for an enterprise deployment. Note that these are from the 2007 documentation:
Enterprise Deployment:
http://msdn.microsoft.com/en-us/library/ms942978.aspx
Base Deployment:
http://msdn.microsoft.com/en-us/library/ms960405.aspx
Good Luck,
Matt Furnari
Commerce Server Consultant