With dSLRs getting popular by the day, chances of these type of confrontations are going to increase. But as long as it is inside a private premise and the owner/management decided no-dSLRs-are-allow-but-P&S-are-ok, there is nothing much people can do but to comply with the policy.
However, it must be said that "no photography" means "no photography". If the management decides to put up a sign on their premises that says no photography is allowed, then it should really mean no photography, regardless of the camera type you are using.
Is taking photos with a P&S not counted as photography? Are people worried that SLR resolutions are higher than P&S cameras? Come on lah. Most compacts today have like 12MP, 14MP, some even hitting the 20MP mark, and if you are using a 1D classic, you have 4MP. No logic.
Of course, the lay man would not understand, and probably would not want to reason. This is the closed mindset of most enforcing officials in Singapore.