Actually, since Steam got rid of the "Don't update this game" setting it's impossible not to update, unless the game offers older patch levels under the Beta settings
You're right. When on earth did this happen?
Not sure exactly when but it was about the same time that they changed some other UI elements, because all the complaints about that got drowned out by thousands of threads full of idiots whining that they'ed changed the colour of something.
EDIT: spelling