It is said the 10k SGD is the highest value banknote in the world
http://banknoteasia.blogspot.sg/2009/01/singapore-10000-highest-value-banknote.html
The next is the swiss 1k.
The USD stopped circulation and printing of currency in larger denominations at the time of nixon.
Ppl have also mentioned how easy it is to sneak in huge amounts of money in and out sg in currency and it is obviously easier to launder money with large denomiations.
for the recording of serial numbers. I read of that before but i read again it isn't true. There isn't any confirmation on it. Do you have some link to show they record down serial for 10k?