Not true. For one of my sites, I average about $.25 per click, but the adwords user is paying $2-3 per click My other site gets about $.50-1.00 per click, and the adwords user pays $18-25 per click. That is according to the adwords tool. I think G takes at least 80%, but that is just my guess from my personal research. Then again, my clicks on the first site averaged $.80 last week
Google takes 25-30 percent. I know because I have gotten $23 clicks many times and the max bid is $50/click. That is almost 50 percent.
It all depends on saturation of your particular market. For example, how many lawyers are still paying $50 for mesothelioma clicks on content sites? Not many I would imagine.... Even if they are, there are so many mesothelioma sites out there, that the top bidders run through their daily budget quickly, therefore the lower bidding advertisers' ads get shown, and you end up with $.25 clicks for a keyword you THINK is worth $50. Just because the top bid is $x, that doesn' mean your clicks are going to pay a % of $x.
I got idea how to measure it. Simply make adword for some fictional word, make page for it with adsense ads and click on your own add, then check adsense stats. Anyone as volunteer?
Due to the smart payout thing that google has, I highly doubt there is any set amount. The amount may differ depending on the cost of the keyword. For those reasons, and others, I doubt they would ever come out and tell publishers the percentage either.
I think there's no fixed share in what google takes. Maybe if you look at it on average you could see a 40% share going to google (which is alot in my opinion)