A little clarification might be in order here.
"The Employment Act" Cap 91
contains the rules governing the employment laws as pertaining to "workmen" generally earning under $1600/mo or others that are not in any supervisory position or handling confidential information.
It is here that the minimums are set down by the Singapore government of 7 days annual leave with an increment of 1 day additional per year up to 14 maximum as well as the maximum work week of 44 hours (without having to pay overtime).
Anybody who falls outside of these guidelines and in not under a "Union" contract (I use the term loosely in a purely local context as they really don't have the power of a "real" union as we know them), have to negotiate their package before signing their contracts. Unfortunately, even that doesn't protect you as most contracts here also stipulate somewhere hidden in small print that the company can change it as and when it sees fit either by memo, addendum or even verbally. This means it's not really worth the paper is printed on either other than to prove you worked for the company at some point.
You have almost no protection in Singapore if you fall outside the purview of the Employment Act or a Union Contract as the whole government is pro-company biased and for the worker it's Cavet Emptor.
However, a lot of companies start at 10 & 14 days (peons & mgmt) or more and going up to 21 to 28 days normally. Banks and Financial Institutions seem to have the best packages though.