It's a potent sign of how low the American political bar is set that gratitude is expressed because a US president says he will ask Congress to vote before he starts bombing another country that is not attacking or threatening the US. That the US will not become involved in foreign wars of choice without the consent of the American people through their representatives Congress is a central mandate of the US Constitution, not some enlightened, progressive innovation of the 21st century.
George Bush, of course, sought Congressional approval for the war in Iraq (though he did so only once it was clear that Congress would grant it: I vividly remember watching then-Senate Foreign Relations Chairman Joe Biden practically begging the Bush White House to "allow" Congress to vote on the attack while promising in advance that they would approve it).
But what makes the celebratory reaction to yesterday's announcement particularly odd is that the Congressional vote which Obama said he would seek appears, in his mind, to have no binding force at all. There is no reason to believe that a Congressional rejection of the war's authorization would constrain Obama in any way, other than perhaps politically. To the contrary, there is substantial evidence for the proposition that the White House sees the vote as purely advisory, i.e., meaningless.