yes I've checked Jensense and saw the news about it being account wide. I think it does not make sense, but if google is really doing so, we can doing nothing about it. We never know but can only guess which site has poor conversion rate.
Here's my experience for what it's worth. 2 of my sites have numerous subdomains. Both of these sites have been with AS since the program began and have extremely stable numbers across the board. Site "A" has subdomains on topics that are closely related to each other. One of the subdomains on this site averages .45 per click with a page CPM of 69.00 and does not get much traffic. Another sumdomain on sita "A" averages .05 per click with a page CPM of 3.00, this subdomain gets a good deal of traffic and is responsible for about 50% of traffic to site A. When I completely removed all ads for a few months on the subdomain that averaged .05 cents per click, the other subdomains on site A did not start earning more per click. It did not effect the income of the other subdomains at all, even after a few months. Another site, site "B" has a bunch of unrelated subdomains. One of the subdomains on this site averages 1.00 per click, while another subdomain on site B only gets about .05 per click. Once again, after completely removing the ads (for a few months) off the subdomain that averaged .05 cents, it did not effect the income of any of the other subdomains on site B. All 6 sumdomains on site B get an equal amount of traffic. Hope that is the information your looking for.