I don't think anyone thinks Putin is directly responsible, in the sense that he gave the order to shoot down the plane (assuming it was a SAM). Indirectly responsible, maybe, in the sense that he's arming a bunch of hotheads down there.
But even then, we can't jump to conclusions just yet until we figure out who shot down the plane, or if it was even shot down in the first place.
Russian commander of terrorists Girkin already admitted they shot down the plane and Russian media confirmed it. The story only changed when it was reported to be an airliner. Case closed.
What we can't speculate or hypothesize here at FR anymore? Dang... stop the presses bubba. :)