You can't say that wikipedia is biased without first reading it (which is impossible considering it's size). However, one can also argue that with millions of topics and authors, it will contain biased articles. I would not be surprised if some of those articles were about the closed-source (microsoft) versus open-source.
Nevertheless, I've used wikipedia a lot and it really contains a LOT of useful information that you cannot easily find elsewhere. I mostly find the content to be clearly written by experts in the field whose only motivation to write something is correctness. Moreover, if an article is clearly biased, then you have to realized that EVERY reader who comes along can change it, and it will be changed in that case. The result is automatically that an article only becomes stable when it gives hard, and correct facts, without being biased.
I'd be very interested to know (and read) the article that Microsoft wanted to see changed, so I can judge myself if it is biased, or that it just contains facts that Microsoft doesn't like to be public.
The big problem in this case seems to be the fact that the to-be editor was PAID. That means he WOULD be biased towards Microsoft per definition
If this guy decides to independently still edit the article, then I think it would be accepted. As long as an article contains opinions however, it's likely to
be changed again and again... They'll have to stick to facts.