Watches like other goods and services - the transaction price is determined by demand and supply. If the demand is high (like Rolex and PAM), you will hardly get much discount. In fact, for some you have to pay premium over the list price (e.g. Daytona). For those where the demand is less than supply, the selling price will likely drop.
So don't feel so good next time you got a big discount, it just mean that not many people like the one you are buying!
Just like my Alain Silberstein - but I am fine with that!