Having using "Pengiunplug" for things like replay FPView for Broodwar, definitely concur with the "a bit of magic" assessment.

I've always been fascinated by how many clever hacks come out of the SC community for adding features/functionality like this. A lot of the SC2 observer mode features were a product of hackers making plugins and utilities that enhanced the replay experience for Broodwar, so it's fun to think about what sorts of nice things will be made by such hackers going forward for SC2 :).