40,000 app-submission threshold, Microsoft's Windows Phone Marketplace has hit another milestone: 50,000. According to analyses done by All About Windows Phone, the Taj Mahal of tiles has seen developers submit just over 50,000 applications for review -- 42,655 of which are currently available in the United States. What may be more telling is the rate at which developers are submitting their wares. Over 17,000 apps have been submitted to the Marketplace in the last 90-days from over 13,000 different publishers (an average of 265 per day). With Apple's iOS App Store and Google's Android Market sitting firmly atop the mobile-app-ecosystem totem pole, Microsoft is looking to close the gap and put distance between itself and Research In Motion's BlackBerry App World. Hopefully, the gang from Redmond can keep the positive momentum going through 2012... even with its next major mobile OS revision being a minor one.