This is only a guess.

There is little doubt that tynon, and evony, 'tweek' the game parameters as the servers come out. In early evony for example attacking npcs gave regular 'finds' for heroes, but then became rearer than ducks teeth.. Tynon I think is doing the same thing, however I an not sure they update the published parameters, so the chance of say blue medals producing an upgrade is higher in server 1 than in server 99, although the published percentage success rate is not changed. As I say, i could be wrong, but it does seem to be the case with me. I know a 1 person smple is not mathematically significant, but thats what I think is happening