When Nike, and Michael Jordan, launched the 'Air' series of basketball and running shoes, which eventually came to be known as 'Air Jordan', it was perhaps the first brand - apart from airlines and sappy pop bands like Air Supply - to use the word 'air' as a brand name or extension. A combination of Jordan's extraordinary ability to 'fly', some great advertising and the presence of a crucial 'benefit' in the 'air' suffix meant that the 'air' in the Nike worked like a charm and sold many millions of pairs of shoes for them. Does the 'air' in the MacBook Air work quite as well for Apple? I think it does.
Apple, I believe, is the Nike of personal computing. Like Nike, it has always been about path-breaking style and revolutionary product developments coming together to deliver a clearly superior product to its consumers. That's why 'Air' is the appropriate brand name for the world's lightest personal computer from Apple. Just like it was the right name for the world's lightest shoe, from Nike. Right, so would 'Air' work just as well if it were tagged to an offering from Microsoft? Obviously not anymore. But what if Microsoft had launched the world lightest operating system (hypothetically speaking, of course) and chosen to call it Microsoft Air? I think not.
I think that after Nike usurped the word 'air' for itself, it needed a company like Nike to take the 'air' back from for other uses. A company like Apple. Not Microsoft.