It is not the number of apps available for Windows Phone 7 that is at issue. It is the number of important apps available on other mobile platforms but not for Windows Phone 7. A few that come to mind are Dropbox, Evernote and Google Voice. Porting an app from one mobile platform to another is not a simple matter. With this in mind, Microsoft announced the availability of resources to specifically help iPhone developers writer software for Windows Phone 7.
Microsoft created a website of resources to help developers for other mobile platforms to write for Windows Phone 7.
This includes a series of articles by Jesse Liberty.
While these resources are definitely a big help, the real test is whether enough Windows Phone 7 devices have been sold to iPhone developers to allocate resources for Windows Phone 7 development. This certainly has not been the case for the apps listed earlier as well as Microsoft’s own developers who have produced great apps like PhotoSynth for iOS that are not available for Windows Phone 7.