Wait a sec, what's happening here is good. TMS has thrown a really excellent, data-based "test" at the theory, and backdraft7 and Shaddows both responded with the relevant information: their sites only started doing this a couple of years ago, and it seems to get worse around known Google updates. Those responses right there: if the rest of the thread hadn't already convinced me what's happening is Google related, those would have.
Now, whether it's something Google's doing on purpose or a side effect of other stuff, I don't know. But does it matter? The effect is the same regardless of the intent.
I think there's a lot of data supporting this theory, and it might be time to accept that it is happening, and it is Google related, and start talking about how to get past it. At the end of the day, that's what matters, isn't it?