Great post Panda. Long time lurker since the BOM days (even remember the epic Superman Returns prediction from Kal-El).... lol
Anyway, one thing to consider is that the Civil War writers prior to the release mentioned that they were okay with losing the Marvel virgins with this particular movie: http://screenrant.com/captain-america-civil-war-marvel-virgins/. Marvel wasn't interested in giving too much of a back-story for the movie.
I think the Cap trilogy had a very linear storytelling, which pretty much forced viewers to watch the previous movies with the many connections. Hell, I haven't even brought my GF to see this movie because I haven't had the chance to watch the previous movies with her (she's never seen any of the movies).
I do not think it's been a problem in general with Marvel movies. You could skip Iron Man 2 and enjoy Iron Man 3. A lot of people loved the Avengers without watching the previous movies. With Phase 3 here, I do not think it will be much of a problem even with the reported changes with Thor, it looks like a movie that you could easily watch without going to see the others. At the end, I think it's about the writing and how Marvel chooses to tell the story. Let's see how it plays out.
As for Infinity War, I doubt Marvel would not include the GA (Marvel virgins). It would be leaving $$$ on the table and I doubt they would be doing that especially with International moviegoers. I think that's been the problem with Civil War, it was made for the fans and not much outside of that. Also, the movie lacked the epic large-scale action pieces and those " fuck yea" fist pump moments that the first Avengers had (With that it's still my favorite Marvel movie). Civil War is a great Captain American sequel but would be a poor Avengers movie with the limited scope.
With that said, 400+ and 1 billion WW is a great result with Marvel knowingly limiting their own potential audience.
