Now you can partially remove quicktime (dragging the app from the app folder to the trash), but that doesn't actually remove it. it only makes it so you can't run the quicktime UI. iTunes still works like that...
but wait, there's more... Since quicktime isn't actually uninstalled, when you run system update, it selects quicktime to be on the list of things to be updated (when there actually is one).. not a big deal as you can tell it to ignore that update.
However, when itunes need to be updated, it sometimes updates as iTunes+Quicktime if it needs new features from a newer version of quicktime, in which case it reinstalls quicktime. This overwrites any file associations you may have changed (i.e. opening avi files with VLC or mPlayer instead of quicktime) back to opening with quicktime. When all it really needed to do was install the new libraries and maybe the front end if it really had to be updated.
But tell me, why the hell is it updating file associations that I specifically changed!