man CU why aren't you in marketing with ideas like that.... probably because that idea is horrible.
If microsoft countered every mac ad, they would seem desperate and defensive. Their new campaign is a much better way to show cost differences between microsoft and apple, which is a good stance to take, because it's obvious they wouldn't be able to win in a campaign trying to show their product as better. They don't even highlight their product in the ads at all... microsoft ads showing people buying HP and Sony computers would be like a milk commercial advertising refrigerators. How about focus on your product, and not the box your product comes in.
The fact is, Microsoft knows that it will never win a windows vs mac argument in any ad other than cost, so that is their focus. Just like Apple knows bringing up cost in their ads would be silly, so they stick to ease of use, and the highlights of their operating system.
How do you propose they counter a mac gets less viruses ad? "ugh, yeah they get less viruses, but with the new vista protector program, you will get less viruses than you did before, although we still recommend buying a 3rd party virus scanner... " that doesn't come off as a very good ad... so they attack the wallet.. and in these economic times, it's a good place to go.
And the apple pile of money wouldn't be larger. Did you hear the amount of money they paid seinfeld for those 2 microsoft ads? it was way more then hodgman or long make for the mac/pc ads... and that was the point of that ad.