Look at it this way -- the Watson system is pretty important in improving the quality of Windows (let's assume that more quality -> more sales). If coders (most of whom work in a corporate environment) ever found out that Microsoft was looking through their code for a non-emergency reason, they'd immediately turn off error reporting on all of their systems (not to mention, file a few lawsuits), removing sources of crash errors from a sector that is vital to Microsoft (and leading to a decrease in the quality of Windows, and thus, fewer sales).

So it's in their best interests to keep those internal controls as strict as possible in order to avoid such a thing.