I think the legalities acknowledge that things change over time. Often there are also disclaimers at the bottom of the screen or page, stating that the claims are based on published data from such-and-such a source at such-and-such a time (which makes them accurate, in this case) If one had somehow broken the law every time one made a commercial that cited one's opponents features, I think this kind of advertising would quickly become completely impossible from a legal perspective.
The ads are irrelevant for a wholly different reason: Microsoft hires lame, fashion-insensible, uninteresting, whiny people who are looking for computers based on a stupid set of specifications rather than actually using them for anything interesting, and tries to argue based upon them that Apple customers are making a mistake. The problem is that the people represented in the MS ads were never going to buy Apple products in the first place, and the people to whom the ads appeal are pretty unlikely likewise to buy from Apple.
I own two computers running Windows and only one running OS X (and Tiger at that). I would buy another computer running Windows (but not Vista), but I wouldn't buy any of the ones that were featured in those ads.