I understand, but US startups have a wrong sense of entitlement. They might come up with the idea, but if their execution falls short why should others be stopped?

I'm not just talking about European startups, but this also happens within the US ecosystem. Take the latest and greatest: SnapChat vs Poke.

Additionally, if a US startup does not service the rest of the world (specially in e-commerce, which is what Rocket Internet focuses on) they are giving others an opportunity; and others have the right to execute this. Take Gilt copying Vente Privee; VP is not calling Gilt a copy cat.

Your "facts" are unfortunately wrong. Most of their ventures are e-commerce sites i.e. not exactly unique ideas, and doesn't even target the European market.