The framework library is between 88% and 96% managed (depending on the
version). I have analysed various versions of the library and present my
results here:

http://www.grimes.demon.co.uk/dotnet/dotnetWrappers.htm

It is interesting to analyse remainder of the library (ie the code that
is not managed). There are several options: platform invoke, COM
interop, embedded native code or internalcall. The internalcall methods
are unmanaged and are provided by the unmanaged DLLs in the runtime.
Embedded native code are actual x86 machine code in an assembly and
although there are a few methods like this, they are actually calls to
unmanaged DLLs, so they are equivalent to platform invoke. Platform
invoke are calls to unmanaged DLLs, mostly the Win32 system DLLs. And
finally there are calls to unmanaged COM objects.

My analysis of the use of COM in the .NET library is:

v1.0
3.4% of methods are implemented as COM interop calls, but 0.35% of
method calls in the IL methods are to COM methods.

v1.1
8% of methods are implemented as COM interop calls, but 0.42% of method
calls in the IL methods are to COM methods.

v2.0
4.2% of methods are implemented as COM interop calls, but 0.21% of
method calls in the IL methods are to COM methods.

As a comparison I have also analysed the Sept CTP of the WinFX runtime
components (6.0.5070) and I found that 2.3% of methods are implemented
as COM interop calls, but 0.2% of method calls in the IL methods are to
COM methods.

From all of this you can see that COM *is* used by the framework
library, but the usage is very low.