Why not? It's like saying "surely, from the guys whose raison d'etre is to research nuclear physics, these accelerator data are not very convincing". These people find examples of media bias and publish them. How the fact that they are specializing in doing it somehow invalidates their results?
Your analogy is not quite correct. I'm not saying Reuters didnt slant those articles in those particular examples but it could be a honest mistake; this site will never report when Reuters slants towards Israel because that is against its raison d'etre, so your examples are unconvincing as to Reuter's purported bias.
