Quite simply, I find "canon" to be those events which the subsequent games decide absolutely must occur within the game for the narrative to maintain continuity. My classic example is how, in Fallout 2, you will come across NCR - which is led by Tandi, and grown from Shady Sands. Which means that, canonically, you had to have received the "good ending" for that town in Fallout 1, and that your PC had to have saved Tandi from the Raiders in that game (or that she at the very least survived...) Anything else, not specifically referred to in subsequent games, isn't canon.
I'm the same way about this, except a little more detail oriented. Canonically Dogmeat died in the Base, and Myron's died (murdered by a Jet addict). For me Myron died before that, and Dogmeat survived. Tandi could have died. When I play Fallout 2, the personal events that conflict with FO2 are set aside without hesitation; There has to be an official timeline to base the next game from.
My canon peeve, is when old [aged] things are drastically different in the future than they were in the past, like all of the Handy Droids never having had six arms, but only three. If you play Fallout 1, Mr. Handy is in the opening titles, In Fallout 2 a Mr.Handy is usually the first real threat your PC encounters (Either the robot or Fire Geckos). When you play FO3 he is unrecognizable (cool looking, but completely different). :shrug:
Is this not like as a http://t3.gstatic.com/images?q=tbn:ImCft5HJcO9d8M:http://images.yogee.com.au/lego_star_wars_Hailfire_Droid_Spider_Droid_4.jpg&t=1 or http://i271.photobucket.com/albums/jj125/Gizmojunk/Cyberman-SketchUpandPhotoshop_DaveThorp.jpg redesign in Dr. Who?
Things can be updated by different artists, and made really awesome looking and
still keep a recognizable appearance.
Just look at http://i271.photobucket.com/albums/jj125/Gizmojunk/TrapJawComplete.jpg from the old He-Man cartoon.
Now look at this http://i271.photobucket.com/albums/jj125/Gizmojunk/Trapjaw20front.jpg...