It's worth noting that the Donetsk People's Republic is strongly influenced by Moscow. "Strelkov", the leader of the militia, is FSB (current/former up for debate). Russia doesn't want an incident with America over this. How many arms did Russia twist or break? Probably a few, but it's what they're good at. Maybe Borodai will get asylum once Kyiv crushes the insurgency, in return for his compliance.
It is also possible that Ukraine did down the plane. I mean, Ukraine lied about having its own anti-aircraft weapons in the area after that, despite the strong evidence of them in Slaviyansk (presumably to deter a Russian air force attack in aid of the rebels).