I don't know if I would say that the E. European models are quite as dominant as it would seem. If you take the top working in models in the word, per models.com, you have Daria at #1 (Ukrainian Canadian), Gemma at #2 (Australian), Julia Stegner (German), Isabeli Fontana (Brazilian), Doutzen (Dutch), Mariacarla (Italian), Hana (Czech), Raquel (Brazilian), Lily Donaldson (Britsh), Diana Dondoe (Brazilian), Eugenia (Russian), Sasha (Russian), Elise (Belgian), Caroline T (Brazilian), Freja (Danish), Snejana (russian), Iselin (Norwegian).
Now, you have the 3 russian girls, Eugenia/Snejana/Sasha, Hana is Czech and Daria is of Ukrainian origin, but that's only 4/5 out of 17. I don't think it's exactly domination. Just as many Brazilians, W. European countries, etc. And if you go further down the list, there are more Americans and Canadians. The big omission is modeling these days are black models; I actually saw lots of black models in NY, but hardly any in Milan, which I think is a travesty.