It's something that does certainly happen, but regional preferences are just as real. For instance, the amount of juice in Fanta across Europe doesn't seem to correlate with wealth at all. Even the sugar contents vary wildly, even across eastern Europe.
For Nutella specifically, there are also differences in composition between the more wealthy European nations: https://www.youtube.com/watch?v=CXp2MTWNoZ4 According to that report, the texture is different to accommodate for the differences in common bread types, which makes a lot of sense IMO.
With how little actual hazelnut goes into a jar of Nutella compared to palm oil and sugar that make up most of the spread, I doubt Ferrero is saving a lot of money selling inferior product to poorer countries. With expensive goods such as meat and "pretty" vegetables, there's more money to be made.