the only place I've been where people check entry stamps on exit are in various dodgy airports south of the Sahara where it is a great way to enhance the miserable income you get.
I've often not had or misplaced the entry paper for the US and Australia and never been asked for it when I left.
Anyway these days they have you via the EPSA or whatever before you filled in before even getting on the plane.
In the past I've posted about entering France at CDG without a check - happened to me a couple of times and from the reaction of the staff when I fought my way back in to get my baggage it was quite common.