Who should write documentation?

Do developers write good product documentation? Is someone who knows a product inside and out the best person to document it?

Have you ever bought a product and you could obviously tell that the manual writer didn't speak the language natively? From my little knowledge of languages it seems that it works better for people to translate into their native language.

I think the same principles applies to developers translating from code to documentation. I would prefer to explain how a product works to a user and have the user write the documentation because they will cover things that seem obvious to me but not the average user.
Someone not intimately familiar with the product will probably write much better documentation.

Do you agree?