I'm assuming that users have their graphics cards set to perform aspect scaling, which is pretty much the best case scenario here. Stretched FMVs would be a blemish too.
Regardless of each user's setup, any screenshot taken during FMVs will always be 640x480 and include the same letterboxing.
It's not just about the screenshots - it's about what actually appears on the screen. In this case, these aren't the same thing, and a widescreen user will see black bars on all four sides.
Absence of correction may be considered a blemish per se, but it can't be rated "flawed" if you get my meaning.
I'm not sure I get your meaning.
This theoretical image:
is objectively preferable to this simulated image of what a widescreen user would actually see:
The fact that it looks like the latter instead of the former means there is a flaw in how the FMVs are handled. The flaw is that the 16:9 FMVs have hard-letterboxing, and are forced 640x480. It would have been better to have them at 640x360, and to have the game's video player scale them to native res, preserving aspect ratio. In fact, it's within Rebellion's capacity to fix this... if they and Valve are OK with all the customers having to redownload about 200MB of data.