The truth is there's plenty of us in the middle still. My two person iOS dev studio has pulled in 6 figures a year for the past 4 years. The problem is not that there's no middle ground, it's that the everyone used to get guaranteed downloads, and with the removal of new releases and the never ending flood of apps, 90% of apps will get just about zero downloads after launch nowadays.
But there's still plenty of room for small studios like us who know their target audience and what works on the app store to make a sustainable business. So I'd say top 0.1% for the insane successes that can support hundreds of employees, but for a small studio, just getting in the top 5% can work.
If you're curious about numbers, check thinkgaming.com, to see that the top 200 grossing game is still pulling ~$10K a day on iPhone in the US alone. When you add all countries, tablets, and Android devices, you start to see you don't need a top 10 or even top 100 grossing app to make some serious cash.
So while it has gotten a lot tougher in the app store and it's increasingly difficult for newcomers with no experience to hit it big, there's still very much a thriving middle ground between the insane successes and the utter failures. I suspect that it's not well known is due to the fact that those in similar positions to us don't want to dish out the valuable knowledge they've acquired through years of experience that could only increase the competition.