It's a bug plain and simple...

These kind of things commonly occur with both companies, it's just a matter of if a site takes the time to complain about it before it's fixed or not.

As for "cheats" both companies were VERY guilty of it during the FX/6800 days. For the most part those days are gone, and now all that remains is drivers bugs generally.

As for image quality by both companies, on a technical level NVidia's is better, that much is a fact. Which you prefer is a matter of personal opinion, but going by paper facts nvidia has better IQ this gen.