Honestly, why go to the effort? With 2 massive competing phone platforms that are implemented sanely, this time it is entirely up to Microsoft to fix any...inconsistencies. They are the underdog, and they don't deserve to have the whole industry bend over and twist their apps just so that a fledgling phone platform is more useful.
I want to agree with you so badly (and to some extent, I suppose I do), but any time I consider the margin of users you could "safely" exclude, I consider the competitor who does not.
On the other hand, any time you consider spending dev cycles to accommodate a minor player in the mobile market, you can consider the competitor who instead makes their product better on the main platforms.
That's like saying that you need to make your website work with Opera, when most people don't bother. In this case, Microsoft is in Opera's place. I'd say it's pretty safe to ignore them.
Kinda a bad analogy as Opera is pretty much on par with Webkit/Gekko. Sure it basically shares the same JS-based quirks as IE, but it has a much more robust and usable error console so I welcome it.
Actually, that means the answer is even clearer for Windows Phone - since the differences are greater, it should have a proportionally larger share of the market to make supporting it worthwhile.
