Hi Archie -
As the compiler doesn't emit debugging information for auto properties, they are essentially invisible to tools such as NCrunch. The metrics view will report 100% code coverage on a source file that contains no code (I'm willing to discuss the correctness of this as I understand that it may be misleading).
However, I agree with your analysis. If a technical approach can be found to solve this problem and introduce coverage markers to auto properties, this would make sense.
Cheers,
Remco