AX 2012 Budget Control can only be used on certain Main Account Types?

During testing, I discovered that Budget Control is designed and limited to only work on Main Accounts that have an account type = Total, Profit and loss, or Expense.  This help article does call that limitation out, but why would that limitation be designed into the product?

http://technet.microsoft.com/en-us/library/hh242453.aspx