As a Singaporean who has never been on a cruise (looks like
DCL might be my first in 2 years from now!), my two cents on a couple of things in this thread...
Currencies - I just had a quick look at the Royal Carribbean website for cruises out of Singapore and they are quoting me fares in SGD (though I have no idea if the payment processor is located in Singapore, as if not then there is still going to be a 1% DCC charge by Singaporean credit cards to book these). I'd hope that a Disney ship home ported in Singapore would be able to quote/charge me fares in SGD too, especially since this seems to be in collaboration with the Singapore Tourism Board...
Tipping - oh goodness I have no idea if tips are expected on cruises out of Singapore, I'd have to check with friends/family who have been on cruises! Tipping isn't usually part of our culture though so never even thought about this!