The tipping ("service" charge) in SG is compulsory! But in the States, the tipping although not compulsory, but you will almost be chased out if you don't give (worst case is the waiter/waitress chase after you)... Also, the tipping will depends on the "class" of the meal.
Think of it like eating in Fish & Co then vs eating in a 5* restaurant. The tipping % differs. So you may still end up paying more in USD.