The problem is that the right would like to make the only issue whether things finally get any better, and to avoid looking at how the war has already been a disaster.
It's a little like a new technique forcing police to keep 1 bullet in their revolver. As police are killed again and again when the bullet isn't in the chamber, finally in an incident the bullet is in the chamber, and they say 'see, it worked!' Well, no, the Iraq war has apparently a cost in the trillions, with hundreds of thousands if not a million+ Iraqis killed out of a population of 28 million, the US has lots a lot of its values in things like torturing, it's set a precendent for incompetent and corrupt starting of war (where could that possibly cause a problem, as Putin prepares his explanation of his own pre-emptive war, and China can't wait to do the same in expanding its power in Asia) - the war has already had a disastrous price, and if it all goes well tomorrow it doesn't change that, doens't mean 'see they were right'.
At some point, it gets a bit outrageous, like comparing Germany's prosperity today and the poverty before WWII to say 'see, Hitler was right on the war'.
The left wants to see the best things now in Iraq. The right says otherwise not because it's true, but because it lets them have something to think they're right on and not pay attention to their having been wrong. Obama's statement IMO is politically calculated to take the wind out of the sails of McCain's expected argument tonight that the surge has only Republican support. McCain may well now be scrambling to refine the speech on that. It also reflects Obama doing what he does a lot (and lawyers know is often a good idea), acknowleding the other's points that have any merit, so when the surge has done some good, why not say so, and not make that the issue.