Such an "adaptation decay" does not constitute a new continuity because its scope of impact is limited. While it can be
interpreted as having a wide impact if it occurs in a long saga such as MegaMan, it is not
practiced as having a wide impact, as each entry to the series will be localized independent of previous localizations. Therefore, continuity exists only in the original work, barring consistent and intentional changes (The name MegaMan as opposed to Rockman).
When Keiji Inafune is asked a question by a U.S. MegaMan fan, which continuity is he referring to? If, by nature of Inafune being CoJ, his comments reflect only CoJ continuity, what is the point of allowing fans of other regions to ask him anything? By your logic, his writings are subject to CoA alterations and thus hold no direct value outside of Japan.
Well, no one ever said it was well-written. >.>
It's barely "written" at all. There are no "U.S. continuity writers". There are the story writers, in Japan, and there's the localization teams elsewhere, who occasionally take a creative liberty. To them it's inconsequential; probably they even believe they're adding a subtle improvement (brotherly robots touching the audience's hearts; reiterating the franchise name more often to drive home the roots of the game). But they don't do that with respect to continuity across the entire saga. Tweaking the same story in localization, which is what MegaMan is, is not the same thing as a total rewrite featuring a new scenario (such as the case with "Raymond Burr" Godzilla, Power Rangers, etc.). The only instance in which I'd accept "U.S. continuity" is when the change is both intentional and consistent, such as name changes, and whatever side-effects they so induce, such as the case in DASH/Legends 2 with the origin of Volnutt's name. Localization is a derivative work, but not a derivative continuity. The original will always take precedence in continuity.
Let's suppose Capcom does the unthinkable and creates a Classic/X time-traveling game. Let's suppose in such a title that X witnesses a few Wily defeats. Lets's suppose one of these is RM7. The fact that in MM7 Rock threatened Wily, does not mean that in the localized version of such a game, that MegaMan X will deem Rock a Maverick, while Rockman X has no reason whatsoever to deem Rock an Irregular in Japan.
Such a phenomenon in localization is hardly exclusive to video games. Looking at some of my favorite monster movies, an alternate continuity would be if, in bringing a story over, one is intentionally writing a whole new scenario. Such as Raymond Burr's character in Godzilla: King Of The Monsters and Godzilla 1985. However, a localization tweak, such as shortening the dialogue of speculating on Orga's spacecraft in Godzilla 2000, does not constitute a continuity change. It's the same story; the localization team (in this case Sony) simply believed that a small tweak would streamline the film and make it more appealing. Future projects will not take this into account.
Except most of us can't friggin' read it, and have to rely on fan translations which may or may not be influenced by the translator.
That is a completely moot statement. The possibility of "influence by the translator" holds true of all translations both official and unofficial. Capcom employees are still human beings and as such may influence translations personally. The frequent use of "Mega Man" in X2 and X3 is one such testament; it ties to MM7's ending as trying to push X as being Rock, a notion which has since been abandoned by Capcom of America and refuted by Capcom of Japan.
I was told that there's no difference between US and EU continuities.
Using your logic, untrue. If you accept the presupposition that there are different Japan and US continuities, then there are most certainly different US and EU continuities.
Not a phenomenon exclusive to MegaMan, or for that matter even to political correctness. The same name kerfunkery goes on between US and EU Fire Emblem games. Obviously it's less common for two regions of the same language to deviate, but it's not unheard of. It is entirely possible for two regional corporations working with the same language dialogue to have different ideas of how best to proceed.
Your logic therefore mandates a separate continuity for every region, dependent on the structure of the corporation distributing the game, regardless of language.