I'm not so sure I agree with this. To me, it all comes down to where the cash is most valuable. On a 0% loan, I'm a firm believe you are not getting a penny of my money until its due regardless of the value of the asset in my possession. You gain nothing by paying it off early other than the satisfaction of being debt free which admittedly is a good feeling.
The same applies to low interest rates. $70k loan at 2% for 84 months would cost you about $5100 in interest. By year 3, you will owe approx $40k in principal and $2k in interest. Regardless what the vehicle is worth, if can make more than $2k over the next 4 years with $40k cash, you need to invest $40k.