Jones is at fault for not accepting the fight(he had nothing to lose at all) and the UFC is at fault for not putting out a better product.
Jones isn't obligated to fight Sonnen, and they can't make him fight, but at the same time, it's not Dana's fault Koscheck got hurt. I bet you anything if this was Koscheck/Ellenberger instead of Ellenberger/Hieron this would have taken the FX slot next week and they'd have just lived with the "shitty card" flood bomb they'd have got. They could have atleast salvaged it instead of canceling it altogether but it's nearly impossible to promote a guy like Hieron who hasn't fought in the UFC in YEARS as a headliner, he's not a guy like Diaz or Overeem coming over.
Regardless of all of that, Jon is the one who said before he fought Shogun "this is Dana's world" and even said he'd fight Rashad if it meant his job is on the line. I'm still a fan of Jon's but he's become a human contradiction and every week he does something to piss people off it seems. Both parties are at fault here.