"the government has limited the denomination because of drug transactions. Also a factoid I heard is that 75% (or somewhere close) of all $100 bills have traces of cocaine on them"

Both those facts were in an article I read not too long ago. I guess you might have seen it also. I think it was all bills, not just $100's, because they contaminate any others they come into contact with, and also the bill counters in banks. So it doesnt take long to spread it to 75%. I bet that must apply to many currencies.