I'm not so sure Yanukovych was pro-Russian, more like he was trying to walk a line between East and West. It's understandable that he rejected the EU offer, as it really was a bad deal, and the recent example of Greece showed that all is not great with EU membership. The US's problem was that he wasn't overtly anti-Russian, and would not serve the US agenda to destroy Russia, so the neocons had to oust him and get people in power that they could control.