The only point being made in the M$ ads is price. Period.
For Mac users, that's a non-issue.
For PC peeps frustrated by crappy customer service, it's a non-issue.
The ads only work with people who lack any intermediate/advanced knowledge of computers (new or first-time buyers. Unfortunately that's a large number) and watch ads without doing their own investigating.
Keeping that customer group in mind, there two inherent problems with the ads. No. 1: They are very far removed from any "Windows" branding. I speak to people regularly who think that Google is the internet, that their Dell is the operating system, or that a Compaq is the internet. Taking Windows out of the ads helps in the short-term, when you 'think Vista' but long-term it hurts since people still get confused about an HP with Windows on it - will it work? Will it load my CD-ROM? Will it...? I remember when I got my first Windows machine, I hesitated horribly because I didn't know what Windows was ... I thought simply buying a Sony was all that mattered. I mean this as inoffensively as possible: It's amazing how stupid people are wen it comes to this stuff. And, No. 2: All they talk about is price. The ads do not address system specifications (unless you call "Does this have a good graphics card?" "Mm-hmm" talking specs). The ads actually do not answer any of the big questions new buyers are going to have w a computer.
Assuming that OSX is just as stable or reliable as any version of Windows, the customer service and better depreciation alone are worth the extra cost. Whether you like the Apple ads or not, they're very effective because they are heavily branded, and the tagline is "It just works." People see the Apple logo and they picture the brand and what it stands for. M$ is shooting themselves in the foot (feet) by taking 'Windows' out of it... then again, since Windows is different than HP or Dell (eg: two entirely separate companies) the ads would be needlessly confusing to new buyers if they tried to involve technical things. Ergo, since Mac users will predominantly stay with Mac and people pissed off with bad customer service or resale value, M$ was left with the only option and had their hands tied.