well if there's any crib deaths, or issues straight out of the factory, then they would be revealed during that time.

The car will also drop significantly in value during that time, so you won't pay as much.

So there is some truth to that.

You want to make sure it has some minimum mileage of course so any infant mortality failures will have already occurred.  Cars generally go through bathtub curve profiles when it comes to issues - generally.  

Having said that when it comes to mileage, if it’s lower you’ll be paying more for it.  For higher mileage vehicles what is important is how it was taken care of, so it’s history.  Did they change the oil at all the recommend intervals?, was it driven hard?, did they encounter lots of city driving or was it mostly highway driving?  Was it well taken care of?