Doubt from BeerHouse starter kit project-AddedBy

Question

I am going through the starter kit -"BeerHouse" (http://www.asp.net/Downloads/starter-kits/the-beer-house/).
It is an excellent work. But, I have a doubt;-
Why do we need to enter the AddedBy (user's login name) in all the tables in the database?
Can we not enter the user's login name in one table (we may have to add a new table - eg: Register_Table(Reg_id, AddedDate, AddedBy)
and use the Reg_id in all the other tables as the foreign key of Register_Table instead of AddedBy.
Suppose, the user wants an option to change the username in the future this approach will reduce the hastle
to update the username in all the tables. Am I thinking in the right track? Can anyone correct me if I am wrong?

Thanks,