I don't think Levi is onto much at all.
Do designers ever say, "Check out my advice"? Yes, particularly in ashcan publishing where it's fashionable to include design notes, but play advice has occured in many rpgs, big and small (many descriptions in D&D's Monster Manuals, for example).
Do designers ever try to guide play in non-system ways? Yes, with background, fiction, and, more commonly these days with indie publishing, artwork, layout and font choice.
So, while I don't think that game designers are not necessarily obsessed with system, I do think game design forums are. In particular, both the Forge and this forum focus on this more than other forums, which shouldn't be surprising. It's common for opposed groups to share many traits and differ on only a few.
Why? The heavy theory work done at the Forge and elsewhere has given the game design community the language and structures to assess game systems. It was developed by gamers for gamers. Other aspects of design work (fiction, layout, artwork) already had language and structures for assessing them, but it developed in non-gaming fields (crit-lit, graphic design, art criticism), and are less common to gamers. We tend to discuss those things we can get the most and best feedback on.