We may never know why Microsoft waited so long to respond to Apple's snarky but effective "I'm a Mac, I'm a PC" television ads.

Windows Vista was released to consumers in January of 2007, and Microsoft's "I'm a PC/Life Without Walls" ad campaign didn't air until September of 2008, after the company quickly aborted those strange, meandering Jerry Seinfeld/Bill Gates commercials. That's a long time. Over a year and a half of relative silence. During that time, Apple mocked Vista and snarked and mocked some more to millions of television viewers.

Microsoft took the high road by not responding, although not necessarily the smart road. It took the high road again when it did respond, presenting earnest ads about the universality of PCs and how they connect people and cultures around the world.

I thought the ads were an intelligent and uplifting retort to the sarcastic Apple ads that were getting tiresome. They made Apple look like a smartass teenager.

But the problem was the Microsoft ads came too late. And they didn't even mention Vista. And Vista had been having problems…compatibility and performance problems…very public and reported problems…for over a year.

As expected, Apple jumped on this, airing a few humorous ads accusing Microsoft of sweeping Vista under the rug. Not that Apple mentions its own operating system much in its ads. But let's face it, it doesn't have to.

In any case, it was a clever response by Apple. Microsoft was not going to get away with glossing over Vista's problems with its message of Windows World Peace.

Apple kept hammering away at this point with this ad.

This spot made me chuckle, as most of the Apple ads do, but it also made me roll my eyes at Apple. And I wasn't alone. Apple is accusing somebody of spending too much on marketing? To quote the great John McEnroe: "You cannot be serious!"

Last week, BNET scooped a story that Apple spent US$486 million on advertising in its most recent fiscal year, compared to Microsoft's US$300 million. "Those Apple hypocrites," I muttered.

But it's not that simple (Is it ever?). Comparing Apple's 486 to Microsoft's 300 is not fair or accurate. It is Apple's total ad budget for fiscal year 2008 compared to what Microsoft spent on just Windows, I mean Vista, err, I mean Windows. Microsoft's total ad budget for fiscal year 2008 was US$1.2 billion. It makes perfect sense that Microsoft has a bigger ad budget. It is, after all, a much bigger company than Apple.

So which company's ad campaign delivered the most bang for the buck in 2008? It's difficult to say with any certainty, though blogger Todd Bishop gives it a worthy shot, breaking down ad dollars spent by each company in the context of revenue. Still, it's hard to say who's winning the ad battle based on any hard numbers.

But ad budgets aside, both campaigns generated massive attention. As far as perception, I think Apple, despite a tendency to be glib, successfully made Microsoft and Vista look slow and archaic. And Microsoft responded too late with a strategy of playing not to lose rather than playing to win.