International emarketing within video games

International emarketing always existed and this even before the popularity of the web.
When I was a kid I had huge difficulties to understand why and how some editors were publishing two version of the same game for two different markets.

Let's take as an example the following shoot'em up:
US and Japanese version:

Contra 3 on Super Nes

The protagonists of the game are human being

European version:

Super Probotector on Super Nintendo
The protagonists of the game are robots.

Here we can clearly see the differences, we may think that the American market more fits with heroes like Rambo where a single human being can face the most horrible creatures. Whereas it seems that for the European heroic behavior does more belong to fiction.