It's not the inaccuracy that matters, it's the completeness. I may write an article about my company and omit the fact that the FTC has fined me seventeen times for cheating customers. When a company PR hack writes a Wikipedia article, you can bet it will present the company in a move favorable light.

This is not limited to companies. Political parties hire people to write Wikipedia articles on even their most minor elected and appointed officials. While naturally unbiased and accurate, they consistently portray the person as a great and brilliant humanitarian and sage.