I'd echo that. When payroll taxes are really tied closely to the benefit that's received through them, that tie can make a big difference in how the benefit affects people's behaviour. When I have Canada Pension Plan premiums deducted from my paycheque, I realize that I'll get a benefit from that later in life.
Also, if that weren't there, I might have to pay a bigger pension plan premium to my employer. So in a certain sense I'm buying something with it. It's not just going into a pot to Ottawa; I'm buying a pension with it. The greater is that tie from premium to service, the more efficient the payroll tax can be.