Since there's the a priori notion that everything on an official product is "canon", you either accept this or not.
The distinction you draw between a “rule” and a “notion” seems to be that the former is something everyone is obligated to agree with while the latter is not. Regardless (since for those who agree on a definition of canon the distinction doesn’t matter anymore), I agree that no one is obligated, as a matter of principle anyway, to accept all the work of EA/Origin and its licensees as “canon”.
But there are important practical differences that explain why many of us believe there is no real choice except to follow where EA/Origin leads. Let’s consider a “what if”. Several WC fans form a rival group with a definition of canon that is limited to the games. (Certainly that would have instant appeal among those who don’t like the movie. EDIT: I actually wrote this post before seeing Edfilho’s latest comments. Sweet.
) So far, so good. But then say a new game is produced that is based on many of the facts presented in the movie. What then? I don’t think it stretches the imagination to predict a debate erupts within our new group. Some will argue the new game is canon (“That’s our definition!"), others will argue it isn’t (“No, our definition applies only to the
original games, period!"). So maybe a few people leave to form yet another rival group that embraces all games no matter what. (Note, by the way, that the first group has increasingly reduced WC lore to a pretty stagnant set of facts, which raises the question of what the real point was to their exercise to begin with.) So now a new movie comes along, and it’s dead-on consistent with the original games and adds several new facts that are also perfectly consistent except for just one or two that derive from the prior movie and the new game. “Well dammit!” is the curse most likely to be heard from members of both groups.
Meanwhile, the rest of us are happily extending and building up official WC lore. And that’s productive.
Since there's no rule to decide what is "canon" and what isn't, the debates to wheatear the movie "fits" or not won't really be productive.
As I tried to point out in an earlier post, the only way the debates are not going to be productive is where people make much of a given inconsistency but their true gripe is simply that they do not like the movie (or whatever it is that EA/Origin has otherwise blessed). This sort of debate, you see, is not about which explanation best accounts for which inconsistency, it’s really about how canon should be defined in the first place. And that will likely prove fruitless, first because those pressing the matter aren’t being honest about what they’re really about, and second because we’re unlikely to be persuaded to abandon our current definition (certainly in part for the reasons just above).
Fan-made theories explaining those situations are an interesting exercise, but they also don't really make anything more official.
If and until EA/Origin recognizes them, that’s true. But those explanations still qualify as candidates for canon, and that’s a very important distinction all the same, as LOAF notes.