There's a difference between "Barack Obama is the Antichrist" and "John McCain is closely tied to George W. Bush" in the realm of negative ads. A dusky-voiced narrator does not constitute an immediate entrance into Willie Horton territory.
Part of it is the imprecision that the word "negative" carries with it. The rationale for voting for one person over the other is that one person is more acceptable to you than the other - and the main reason they're more acceptable is because the other person did something that tarnishes their case for your vote. There's a common-sense definition of "negative" that pops into our head when we hear the word. It's the Harold Ford 2006, Swift Boat-style of ad that's filled with rank dishonesty and needlessly personal attacks. In the current media environment, though, where you aren't allowed to say one person's doing something wrong without finding an exact equivalent on the other side, "negative" becomes virtually any ad where you mention your opponent by name.
What sucks is that the ad (which is not only entirely true, but uses clear, unadulterated statements from McCain to said effect) is light years away from the Celebrity ad - Obama fails to compare McCain to a woman who lost both of her children in a custody battle due to very public substance abuse issues, for instance. Although I wouldn't mind if he compared McCain to Mario Lopez. Because Mario Lopez sucks. Really, that's it. "John McCain: The Mario Lopez of our time." I think it'll sell.