Yes, all three say that diplomacy is the preferred means of dealing with Iran, but that a military option is "not off the table". It's not a matter of black ("We should nuke them fuckers right now!") or white ("Military force should never be used! Peace and love will find the way!) but a continuum of shades of gray.

I personally feel that George W. Bush's attitude is somewhere in the charcaol gray zone. He'd love to invade Iran given any pretense if he only had the resources to do it. Obama's attitude is more in the dove gray area. He genuinely sees military intervention as a last resort, but doesn't rule it out as a possibility.

Single sentence sound-bite quotes can make both attitudes sound the same, but they shouldn't be taken in isolation. They should be considered within the context of the person's entire history of both statements and actions. George W. Bush has already started one war for extremely dubious reasons while Obama vocally opposed starting that war. That means the two men have fundamentally different ideas of what constitutes justification for use of military force.

When Obama says that military force is not off the table, but should be seen as a matter of last resort, I believe him. When George W. Bush says the same thing, I don't. In a way, I'm glad that US military resources are stretched so thin by the wars in Afghanistan and Iraq. It's probably the only thing that's kept the fool from invading Iraq already.