right question, I can also give a useful answer until I know which segment of motors we are discussing right now...
1 - Japanese / European / American Wet clutch Bikes
2 - European / American bikes with dry clutch (Slow Engines)
3 - Super Sports / Hyper Bikes (high RPM)
4 - Asian, Latin, African small cc daily comuting bikes
6 - Scooties & Mopeds
7 - Chinese - Yet Quality Bikes (still lower then rest of above)
8 - Chines - 3rd class bikes with poorly reverse engineered or replicated engines.
Each of this segment can have its specific type or recomended oil coupled with the Country and its over all useage and weather.. every thing adds up.