You're not likely to find much of a direct statement from companies about this, because they don't have to say anything. Your question is covered by the base trademark laws and fair use. (At least in the US. Other countries may have different arrangements, or no such concept at all, but that starts moving out of our scope and requires your own research if applicable.) Plagiarism Today has a decent overview of what trademark is intended to cover(and hence what you're not/allowed to do with logos), though it's combined with copyright, which people may confuse it with. The short version is that as long as you're not using the trademark with the intent of confusing or misleading people, such as implying that Microsoft endorses you somehow, you're generally safe.
Incidentally, though, from the Microsoft page you already linked in your question:
However, no license is required to use Microsoft names and trademarks to accurately refer to Microsoft software and services.
All it seems you'll be doing with the Powerpoint icon, as example is to indicate "this is a Powerpoint file." Go nuts. You have the entire web already doing it as backup if Microsoft decides to sue you. (They won't. They don't care.)