My dad's 2010 4Runner dropped a valve into the motor with less than 5K on the clock..
Every manufacture is going to have bad parts in a given lot.
Toyota pretty much invented AQL and every major manufacture uses it today regardless of what they are producing.
http://www.qualityinspection.org/what-is-the-aql
Personally I would have made Ford take it back and switch me out after the 2nd one popped.