You guys forget something. The little amount extra in your check to make sure you break even probably isnt enough to really notice. So, would you *really* invest it? Whereas, a nice fatty check is an excellent way to save up for soemthing. Say, a vacation. Or a new fence for the house. Or down payment for car. Its like a savings account you never see, and more importantly never have access to.
Dont get me wrong, I realize the Fed is makin interest money from YOUR money. But, alot of people wouldnt take the time to take out that extra money per paycheck and invest it and it would end up spent on little crap like dinner at the nice place.