“With regard to existing applications: today’s Windows Phone applications and games will run on the next major version of Windows Phone. Driving application compatibility is a function of Microsoft’s commitment to its developers. Regardless of what we release in terms of new developer features and functionality, we have made a large investment in protecting your existing investments.”
Hopefully that managed to allay fears and doubts that Windows Phone 7.5 developed apps will be compatible with Windows Phone 8. In any case, details surrounding the Windows Phone 8 remain scarce at this point, but we can safely assume that additional details will be revealed as the update gets closer to its release whose release date at this point remains somewhat of a mystery.