When Windows Phone 7 launched in the U.S. earlier this month, Microsoft announced that it already had 2,000 apps and 13,000 developers registered to build software for the platform. Two short weeks later, the proud Redmond giant is boasting of 3,000 apps and 15,000 registered developers. That’s some solid growth for a new, unproven platform. It should also be very encouraging for consumers — yes, established platforms like iOS and Android dwarf a growth rate of 500 apps per week, but mobile developers are spread thin. To know that Windows Phone 7 is drawing a fair amount of developer interest in its infancy is very, very comforting. As we know, Microsoft needs developer support if it hopes to succeed.