related: http://scifi.stackexchange.com/questions/8335/why-are-there-only-2-universes-that-are-visit-able

It seems that there are differences in the universes dating back to the 1930s

 * Zeppelin flight was effectively finished in the USA by the [Hindenburg disaster][1]
 * Gaudí's [Hotel Attraction][2] was built over there.

Given that these differences and the duration that they have existed I would expect the two to differ much more. 

The lack of heavier than air flight over there, would have significantly altered history, the course, duration and victor of WWII in the very least. Which would have global knock on effects, imagined over 60 years. While I would expect some similarities between the universes, they seem almost identical. 

Is there an in universe(s) explanation as to why there is so little deviation between the two universes?

As a bonus, is there a known diversion event that initially separated the two universes, or have they always existed mirroring each other.


  [1]: http://en.wikipedia.org/wiki/Hindenburg_disaster
  [2]: http://en.wikipedia.org/wiki/Hotel_Attraction