I really really love this astute-as-hell closing passage from this post by Tom Shone (the whole thing's worth reading, so go do that) (via) about why we're seeing several of our Summer blockbusters suddenly set mid-last-century:
"Taking us back to the second world war (Captain America), or the cold war (X Men), constitutes a rejuvenatory return to a period when plots came in smaller, more maneagable sizes and a nuclear bomb going off actually mattered, if only for reasons of historical continuity. Each film must leave the world exactly as the history books found it — a worthwhile discipline and a useful way of stemming megalomaniacal plot swell.
Last but not least, you will not wish to slit your wrists after watching them. Recent years have found cinema-goers clamoring for an end to war-on-terror subtexts (The Dark Knight), debates on the efficacy of torture (Star Trek), and jingoistic celebrations of war in the middle East (Transformers) alike. The retro blockbuster instead signals a return to the innocent boosterism of the forties and fifties — the golden age of comics — when superheroes wore the American flag unironically, busted Nazi /Communist balls without having to worry about blowback, and stood astride the globe like the gentle giants of the American psyche they were. America gets its own origins story — a psychic reboot."