related: https://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 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. This 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 for why there is so little deviation between the two universes? Fringe as a show is normally quite good at the science in science fiction. While I appreciate that there are plot and production reasons that the two universes have to be closely mirrored, it would seem that there is a deliberate attempt to have them mostly the same but not identical. I have not as yet seen an in-universe explanation for it. It may not have been explained yet, or I could have missed it.  

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