Hi Keith
Microsoft is funding the development of popular apps in a Windows Phone version, so you might get some free cash from Microsoft to do Scrivener for Windows Phone too.
On the other hand, it would be kind of scary committing to a platform where the OS maker is paying people to make apps for it. 
If one were to assess this as an isolated characteristic – which it is not – then one could pity Microsoft or find it scary etc.
But, if you see this with brutal market-force realism – that the first to market (iPhone and Android) usually have an unassailable advantage, of having more apps because of being in the market longer – then Microsoft is using its bute, financial reserves to catch up in the apps numbers.
If you see this as a permanent thing, then you’ll find it scary. But this isn’t forever. Microsoft only needs to pay for enough major apps, sufficient to catch up to a certain critical mass of apps, then it can generate its own momentum once developers see the Windows Phone platform as viable.
This is not a reflection on Microsoft. After all, at the same timeframe, MS actually has more apps than Apple and Android did. No, this is a reflection on Microsoft being late to the market.
Sure, it’s embarrassing, but in a war, embarrassment counts for little. By spending out of its mountain of cash, Microsoft is probably the only competitor that can challenge the duopoly of iPhone and Android.
Remember, the war is not on how good the phone is. The war is how large an ecosystem goes along with the phone, i.e. number of apps, and cloud services. Hence, for Microsoft to use its vast cash reserves to build up its app ecosystem is a desperate – but zero-other-options approach, for any party that is aiming to displace the top two ecosystems.
But if there is cash available for doing something you were going to do anyway, let that be Microsoft’s problem! 
Yes, therefore Keith should strike while the iron’s hot. I don’t own a Windows Phone, and don’t intend to, but in principle I’d be nice for Scrivener to be available on all major platforms.
But why was Microsoft late to market? And remember that we’re not talking about being late by a few months, but by years, in an industry where new products appear and die off as fast as fruit flies.
The answer to that question, more than the amount of money Microsoft throws at it, will determine whether the platform really is viable.
I’m reminded of Bing, introduced with similar fanfare, with similar pay-for-use incentives. Nearly three years in, Microsoft is still pretty much an afterthought in the Internet space.
Katherine
(Full Disclosure: I have an Android phone, and would much rather see Literature & Latte invest development time on that platform first.)