I've noticed this as passenger on some flights, seems to me to be cultural though with my limited sampling I may well be wrong. Lots of clapping on internal flights in South America though I've also noticed it through mainland Europe and China.
Oddest one was an Singapore A380 flight SYD-SIN the day after world youth "day" finished. A couple of nuns at the front of main deck economy started clapping and it took about two seconds for the remainder of the cabin to join them. Don't usually get much applause on that flight but perhaps the faithful were still in party mode...