They do pay 78% as a total, but their network partners may earn a higher percentage and regular publishers a little less, or everyone may receive 78% - they do not disclose this. What is a fact, is that google winds up paying 78% out. It's right in their financials.
I'm not sure who this is, but I don't recall ever stating this. My best guess is that Google keeps the greater portion, but I don't really know. Joel
Awesome how so many people here post some figure they pulled out of their ass without bothering to quote a source. "I heard this there", "I heard that here" etc. won't make anyone believe you.