While Vettel did the fastest lap that was 8.5 tenths quicker than Hamilton's; I don't think that tells the full picture. McLaren I don't think are THAT far off. We need to remember that Vettel would just be taking it consistently and ensuring he doesn't tax the tyres too much; while Hamilton would have been maximizing his corner exits and entries to defend.
In qualifying the nose was very strong I agree - and yes Hamilton was using the rear to spin the car around quite a bit. Hard to imagine Button doing that though; given his driving style
While 10 points might not equal a second, don't forget that this was 10 points all localized - all in one place; the front. The direct loss of downforce might not have been enough for 1 second, but the resulting loss of balance, and understeer, would mean that the fronts would be scrubbing off speed a lot, and you can't take the corners as fast - it's not just a general loss of downforce that you have to account for.