It adds up very well with my experiences. If I add more topic A pages to my site, topic B pages gett less traffic/exposure(?) then before and overall traffic level stays the same. I was always convinced that a page "can`t make it on its own" and that the "it`s all about pages, not sites" mantra was wrong years ago.
Like Pagerank there seems to be some kind of "Exposurerank".
1. Onsite/offsite factors:page-->Exposurerank
2. Sum of all Exposurerank on site-->max. exposure allowed:site
3. Max. Exposure allowed-->traffic/CTR measurement:site and pages
4. Traffic/CTR measurement:pages-->redistribution of Exposurerank
5. Traffic/CTR measurement:site-->adjustment of sidewide Exposurerank
6. Changed onsite/offsite factors+redistribution(4.)+adjustment(5.)-->Exposurerank
The tricky part would be 6.: If you allow webmasters to add shallow pages without negative consequences, the whole calculation gets worthless.
So Google needs stable rankings and webmasters in fear of adding shallow content and therefore disturbing/exploiting the calculation.
This doesn`t mean that Google isn`t after shallow content, excessive ads or whatever.
But maybe many of the things often seen as cause are in reality only effects or much more effect than cause.