Editor’s Note: A few readers commented that these numbers are actually higher because they include free trials. We talked to Xyologic and found that this is indeed the case, so this changes the conclusion of the story. Nevertheless Windows Phone is still showing strong download numbers given the size of the platform. Always feel free to reach out to us with your thoughts at mail AT insidemobileapps DOT com.

Microsoft’s Windows Phone platform may be just a fraction of the size as Google Android. But it appears to be doing just as well with paid downloads for mobile developers, according to data from mobile research firm Xyologic.

The top paid app, Fruit Ninja, originally created by Halfbrick Studios, saw an estimated 49,800 U.S. downloads at its $3 price on the platform in January. When we covered Android’s platform a few weeks ago, the top app, Electronic Arts’ Need for Speed, was seeing an estimated U.S. 68,000 downloads per month at 99 cents.

That means Microsoft’s smartphone platform, which arrived several years late to market, might prove more lucrative than Android when you consider its size. You also have to consider that Microsoft has been paying top developers to create applications for the platform. While we don’t have exact data for the total number of Android and Windows Phone 7 devices that are in circulation, we can look at the number of Facebook users for each smartphone client as a proxy. Facebook for Android has 27,108,665 monthly active users while Facebook for Windows Phone has 361,145.

Mobile analytics firm Flurry is also finding that developers are starting to bite, with Windows Phone 7 project starts up 66 percent during the past week. This comes on the heels of the company’s tie-up with Nokia, which could bring greater distribution to Windows Phone 7 at several price points.

Microsoft has cultivated deep expertise in gaming and payments through its Xbox business over the years, while Google is just starting to learn how to work with game developers. One interesting thing to note in this month’s ranking is that more than half of the top 15 apps are published by in-house label Microsoft Game Studios.

Meanwhile, paid downloads on Android have been poor so far because the platform has lacked an adequate payments infrastructure. Unlike Apple, Google doesn’t ask for credit card numbers upfront when a consumer activates a new device. It only recently secured direct carrier billing with AT&T and T-Mobile. Culturally, Google’s forte has always been in advertising, so it has been encouraging developers to pursue this revenue route instead of others.

Windows Phone 7 App Downloads for the U.S. in January