That is true but some modes of transportation and some countries are less stringent about this. So a trip to turkey and flying out to the US from there without entering the EU again could save them the hassles and possibly some money.
Originally Posted by
catocony
Look, he's already overstayed his permitted time. Schengen is Schengen. The reason it's one big happy continent is because the entry/exit and visa requirements are harmonized between all the countries. Whether they depart the Schengen zone from Greece or Germany or France or wherever, he'll be flagged on exit.