Everyone knows two things about Windows Phone: It’s a fine platform, and it’s far too small. Users of Windows Phone will sing its praises, but the problem remains that there are far too few users, in total.

This creates a tricky spot for developers, as to build for the platform is akin to setting up a hot dog stand at a minor league ball game, instead of the major league game down the street; you might be working to hit the wrong audience.

Microsoft has a strategy to fix that: tying Windows Phone 8 development to Windows 8 development. In short, the company is working to take the momentum of Windows development, and tie it to Windows Phone, boosting the total work that will be done for its mobile platform. Why does that matter? App quantity and diversity are key to a mobile platform’s life prospects; too few apps, and you can write a mobile operating system off.

Thus, Microsoft wants to ensure that Windows Phone is richly app’d. Now, to what’s new: Enter Steve Ballmer, this morning:

We bring a developer platform and the store in a common way to both Windows 8 and Windows Phone 8. We’ve done a lot of work to standardize the foundation, to give developers across the family of devices the opportunity to monetize their applications in amazing ways. One year from now, between Windows Phone 8, Windows tablets and Windows PCs, we should see close to 400 million new devices running those operating systems.

Those devices represent the single largest opportunity available for software developers today.

I’ll bet you right now that the next app developer to hit it really, really big will be a developer on Windows.

The thread is obvious: Developing for Windows 8 and Windows Phone 8 is similar; there are going to be oodles of devices out there to develop for (400 million!); you will get rich building for the two platforms. What that boils down to in practice is equally obvious: Building a Windows 8 app? You’re also building a Windows Phone 8 app.

This boosts the mobile platform, employing nothing more than the natural momentum of a new Windows release. Windows Phone needs the help.

As you know, Microsoft is revamping Windows Phone with its ‘8’ release, moving not just to a new homescreen design, but also to a shared core with Windows, allowing for development to be cross-platform in a very real way. Some tweaks will be required to move you from Windows 8 to Windows Phone 8, but it will be possible, and quick.

In a sense, the company is throwing itself a lifeline. Let’s see if it works.