Why are you suprised that 4400 is no longer available? It's a generation old now, and long OOP, so finding it should be hard, and the only availability should be NOS parts, 4500 is also obsolete at the end of this year, with the introduction of 4600 for 2012.
Can't see why you are having an issue using a RD4500, unless you are running a rear cassette which is over the capaicty of the RD. The Capacity of the RD should be stamped on it, and a GS should take a 12-32 with no issues, so guessing you have bought the SS version, have you also checked that the hanger isn't bent?
It's pretty simple to work out which one you have visually, the one you have listed from Ebay in HK is an SS, as it's got a very short cage, the GS is like the one in the Chainreaction link, which has a cage which is about 10cm long.
Why should the Compatibilty chart show 4400 parts?, 4400 is long OOP, and 4500 has superseded it (and this will be superseded for 2012 with 4600), maybe you need to do some more research before spending money on parts?