It would actually be very beneficial for MS to have a Mac writer version. All you have to do is to simply keep the Mac app “one version behind” the windows app.

Three things happen:
1. The product (although one version behind) is still one of the most powerful applications for blog writing. So it’s still very much useful.
2. The Mac user who’s used to always getting the latest and greatest (sometimes by standing in a long (!!) queue for hours) starts to see the value of Windows platform (and the shortcomings of staying with Mac software)… (although their hardware is friggin’ awesome!!)
3. Alternative products (paid or to a lesser extent… free) with similar functionality for Mac get heavily disincentivized with possibility of MS getting significant control over this product area on Mac. (Especially since Mac is all about consumer-focused apps. So this app is pretty critical.)

You see, MS really doesn’t need writer as a differentiating point on Windows nor will Mac stay without a writer-like app for very long. So it makes sense for MS to fill the gap* (version-1) and let those guys know that “you can run from Windows… but you can’t hide” :) … assuming doing so is not too much work.

One might have some ethical qualms, but MS gets regularly bashed for doing the ‘right’ thing (openly disclosing vulnerabilities is one of the primary reasons for bad name for MS in recent years despite having most advanced security features across OSes… and vulnerabilities? You just need one, and they all have that!)… at the end of the day, I just ask, is it perfectly legal? And proceed… (to either attempt to fix or “follow” the law.)

Windows 7: 120$
Snow Leopard: 29$
Control over competitor’s user experience (while pushing Live ID and Windows Live Spaces): Priceless!!