Haha.
Well, the blame for this is more than likely going to be taken by an individual, not the corporation themselves.
I very much doubt that Microsoft has warezed programs on their computers, and if they do, it's the fault of the person that installed them, not Microsoft themselves. Whoever was responsible for making those .wav files will most likely be fired.
MS can't check each and every file manually for this kind of thing. For example, i have 16,380 files in my windows directory in 795 folders, it would take roughly 70 hours (given 15 seconds per file) to check each and every file, that's pretty much 3 days constantly checking, that's just not humanly possible, given the rate at which they must update those files too.
As for the distribution of those files, well, the files themselves aren't illegal, they just serve as evidence that someone has done something illegal, if the company that own SoundForge do attempt a suit, i doubt very much that they will win.