The US government disagrees with you as of today (march 24, 2003) with the following travel advisory about Singapore:
"Americans residing in or traveling to Singapore and neighboring countries should therefore exercise particular caution, especially in locations where Westerners congregate". See http://travel.state.gov/singapore.html

By contrast, for Hong Kong there isn't this recommendation for "particular caution", so for whatever reason the State department thinks Singapore is less safe than Hong Kong (or lots of other countries). Even safer is their categorization of Australia. For those interested in assessing travel risk the State department site makes fascinating reading. I consider Singapore to be completely safe, but there are dozens of countries that are safer than Singapore!