This is my POV. YMMV warning.
Here in Malaysia, it's all about relationships and how well you know your AD or gray dealer. On higher demand watches like Panerai, IWC, Rolex or Omega; if you walk in off the streets like a tourist or a visitor, you basically get "katuk" and slaughtered with minimal discounts if any. If you have a good relationship or a "lubang"; you are in good shape - you get as much discounts as the relationship can bear.
Singapore on the other hand, luxury watch shops and used watch shops are everywhere. There is enough competition that every single sale is valuable to the retailer. You get good discounts off the bat. An advantage is that price quoted is listed with GST added, which can be claimed back from the airport. This is a 5% to 5.5% price advantage off the bat compared to Malaysia's prices. Factor in the discounts, exchange rates, credit card fees - I personally calculate for a non-KL (Penang) guy like me; I get cheaper prices in Singapore by several percentage points.
Europe - less experienced. I have several Stowas that I bought retail at the Manufaktum German stores (the only retailer that carries Stowa). They are substantially cheaper than if I bought them off their website because I can reclaim GST at the airport.
US - My brother in law bought several high end TAG Heuers in Las Vegas at a 50% discount sale. The shopping mall we went to also had a Movado boutique which sold Movado, Concord and Ebel watches at big discount rates. When you find a sale, there will be huge discounts. Remember to factor in sales tax credit card and exchange rates. FYI: we went shopping here:
http://www.premiumoutlets.com/outlets/outlet.asp?id=58