Perhaps not Mountain Lion per se, but by your own description it effectively turns the top 10 into a top 9, and for no reason. Now, when that is expanded to the point where the practical reality is that non-apple apps are basically competing for two slots in the top 10, then yes, you start to feel like maybe not that much software is being sold on the Mac App Store. When a spreadsheet program that hasn't seen a major revision in 4 years still chops the charts, yes, it feels like its probably not worth it.

More importantly, as a user, I've simply become blind to the top 10 charts on the Mac App Store completely. I have no desire to visually scan for the 2 apps that might be different.