Personally, I think they were all too big on talent and ego to make it last. Early on, they had a united goal of being the "Toppermost of the Poppermost", but once that was accomplished, and they had time to go out into the world, they started to become their own men (with new, and different intersted - you can even see/hear it in the later music that they had differences in styles they preferred). And, as Eddie mentions, they all started to realize they were talented enough to lead their own musical careers.
Don't know if it is true or not, but I've heard that Hitler actually had a fascination with the occult and things such as the Ark of the Covenant and the Holy Grail. Wouldn't that mean Captain America and Raiders of the Lost Ark were just making reference to history, rather than one giving a nod to the other?
http://bbs.boingboing.net/t/heres-the-amazon-drone-that-will-deliver-america-to-complete-sedentariness/57056/14?u=thekaz
http://www.youtube.com/watch?v=bdTELokKfCk