To answer a few things in here:
His retirement was only announced in the closing weeks of this season. Whether it was planned last summer or not, we may never know (but as midds correctly surmises, there's an autobiography on the way I believe).
For cautions, some referees still like the old notebook system to write everything down, but at the top they tend to use tick boxes and write on cards. The problem in this instance was that when he showed one of the first 2 cautions to Simunic, he ticked the corresponding box on Australia's side (Craig Moore). For once in his life, Moore hadn't already been booked, so Simunic stayed on until he got his third a few moments later. Had Moore been old and slow and fouling as usual, it'd never have happened. Probably. But he messed up.
He's no longer doing Finland vs Belgium, duties have been passed to Mike Riley.