I'm certain they also do un-notified security updates regarding possible exploits while they never mention any of it. They just bake it in under 'Improved the playback quality of some PS3 format software' (which is a standing point in their change-log). They don't really mention what they do. I think there are alot of secrets regarding their firmware updates, probably hoping people will think their games will play alot better if they update
It is kind of ridiculous how controlling Sony is with our consoles. Skip updating and you can almost do nothing!