An updated version of my Myth of .NET Purity rant is up on MSDN. I recommend you show it to your boss if you're being force to justify why your solution isn't 100% .NET.
Summary: Does a solution written for Microsoft .NET have to be 100% .NET? Scott Hanselman looks at how hybrid managed-unmanaged solutions are really the norm.
Here's a few choice quotes, IMHO: ;)
I've heard it said by many a CTO in many a technical briefing that, "We're planning to port our whole system to .NET." Why spend 18 months converting your application, so you can arrive at the endpoint you're already at?
The .NET Framework Library itself isn't "pure .NET," as it uses every opportunity to take full advantage of the underlying platform primitives.
If Microsoft were to truly virtualize the machine, they would have marginalized their investment in the Windows platform.
Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. I am a failed stand-up comic, a cornrower, and a book author.
Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.