you are not understanding the issue here. we are talking about the windows API - they have supported every aspect of it in a backwards compatible way since its inception.

read the Raymond Chen blog about how they used SimCity as a benchmark to test if their backwards compat was working. Marc Andreessen is even on the record as being an admirer of the Windows backwards compat work. they put a lot of work into it and placed a high value on it because they did not want to break developer trust.