All Lufthansa, Air France, Air Berlin and all other airlines crew's are not getting customs / stamped passports because airlines having a special agreement with ministry of foreign affairs.
Not quite correct i believe, we do not need a visa, a gen dec (and a passport) is enough to enter the country. However they usually still stamp our passports, but they try to not use up too much space and can fit quite a few stamps on one page. Sometimes they stamp a piece of paper instead and put that in the passport and remove it on leaving the country. Some of our pilots are not allowed to operate to russia however, apparently non-eu passports are not accepted, especially US ones. If we stay on the aircraft for a return flight (quite rare) we do not have to get our passports stamped though.