1. Bush's SOFA contained the withdrawal deadline, not anything Obama negotiated.
2. Iraq refused to agree to a new SOFA that continued routine troop immunity, so that was that. You might be willing to send them into that type of legal minefield, but thankfully Obama was not (I doubt Bush would have either).
This tack taken by right wing media is not only propaganda, it is simply stupid.
Also: Iraqi Status of Forces Agreement referendum, 2010 - Wikipedia, the free encyclopedia
As to what Panetta has to say, he's got a book to sell and I don't think this is the first time he's stabbed the administration in the back. Maybe he's right, maybe he's wrong, but at the end of the day he's just giving an opinion based on nothing but his own interpretation, recollection, and version of events. Shoulda/coulda/woulda is not an effective argument.