the reason is simple.
Most excel users learn from trial and error....not reading a book.
When a beginner or intermediate excel user wants to write a formula
they will usually start with the "Autosum" button in the toolbar.
Immediately the formula starts with SUM(). As a beginner many people
will assume that this SUM() is necessary in order to calculate the
equation.
As time goes on and the user become more advanced this idea sticks with
them.
So it's Microsoft that is in a way misleading users.
