Just to add my data point. I regularly transit DME on the SQ ARN-DME-SIN // SIN-DME-ARN flights. I've used both an Australian and an Italian passport and there are no problems with needing a transit visa. Even if I'm near the tail of the queue it doesn't take long. There's a check against manifest (I think), numerous checking of passport and BP and security. Each time I've also been provided with an invitation to the lounge. (Flying J.) It's all quite painless.

They seem to be quite thorough and last time there was quite a drama with one passenger being taken away who was trying to enter Russia without a visa. Fair enough too.

It's not a large airport with just a few shops, bars etc airside. Duty free prices on booze are pretty good.