It appears you have NEVER used showdown. The IV spreads have just been added. It is more aesthetically pleasing, and is more user-friendly in choosing your pokemon. Why care about how the pokemon got the move? You are not playing in 3DS. Plus the battle animations are much better in showdown.
As fun as the "Showdown vs PO" argument is, the actual reason why Ame made the switch was because PO was very slow in updating for Linux. The server is run on Linux, and it was incredibly buggy. Linux showdown apparently works fine.
