Re: What would Apple do?
Let me put it like this: I have a Microsoft mouse that I used to use all the time with earlier versions of OS X.
Since I installed OS X "Lion" last year, said mouse has been relegated to the status of "game controller". I haven't plugged it in more than a couple of times this year—both were when I had to work in my MacBook Pro's Windows 7 partition for work. Once you've gotten used to the multitouch trackpad and its power over the GUI, the reason for Apple's GUI changes in Lion make a hell of a lot of sense. And Apple sell rather more laptops than desktops these days, as even Apple themselves will tell you.
The Window market is also moving away from desktop boxes and towards laptops. Some Windows laptops are also fitted with similar multitouch trackpads. In that context, Windows 8's "Metro" also makes a lot more sense. (Also, let's face it, the Metro UI is just another change to the Windows Start Menu. This is an element of Windows that has changed, sometimes quite dramatically, with every major release of Windows! It's a launcher on steroids, not the end of the bloody world!)
As for your assertion that the Mac is a "niche product" compared to Windows: you might want to look at Apple's market share of the consumer PC market, as that's the only market Apple have traditionally cared about. (They're more than happy to let Microsoft deal with the big corporates.) Apple's share of the consumer PC market is a hell of a lot more than the 10% usually bandied around by the usual stat-munchers, because their statistics invariably include all those PCs rusting peacefully in every office block on the planet, rather than separating out the consumer sector from the corporate sector.
Quite how they've gotten away with this deception for so long escapes me, but I suspect Apple don't really care: as long as they're making all the profits, they're more than happy for the media to think they're still the "underdog".