I am truly believing that Adsense is just a good springboard for serious publishers to get their businesses off the ground. Once a site is established to an extent where it can afford to let go of the 'A' and extend out to advertisers paying CPM or a flat monthly banner fee, I believe it turns out much more profitable. Best example: Tech Crunch. At least $70,000 in monthly ad revenue, you can see that Adsense had to move down from the hotspots on their site. Granted sure, Adsense is an easy way to monetize your traffic, but once you achieve a certain growth, I think it's better to play your own game.
My sig is about my own experiences when I removed Adsense from my main blog. The whole Adwords marketing thing is about buying up traffic for pennies and redirecting it to affiliate programs and making dollars. If marketers can make a profit doing this, why can't we? All we do by having Adsense on our pages is to give Big G a slice of the pie.
Adsense is simply too unpredictable to trust more than 10% of your total revenue with. And you're such a small peon to them that they really could care less about booting you for any reason and just claim it under their catch-all "invalid clicks" excuse. When your site has achieved enough traffic (say, 100s of thousands of pageviews a month, at a minimum) it's time to expand out into CPM and selling your own ads, or if you don't want to, you can get a third-party network to do the selling for you.
Check their advertising page. Each 125^2 button sells for $10k a month, two month minimum. Currently, they display 7. Do the math.
I agree with your main point, but what you say here is a pretty big assumption. Those could be friends / partners or even their own sites, etc.
The switch to selling your own ads may be problematic though, even if you are a big publisher. Getting the right people to sell the right product, willing to pay your prices, that's the tricky part. I am standing close to taking the dive, hence I speak out of experience. I can't agree with your "booting" argument though. I've been sending a lot of clicks to Google, and they've treated me fairly and have been quite supportive in terms of helping me optimize my layouts, placements and such. They have yet to boot me randomly. Nor do I think they'd ever boot significant publishers. And by that, I don't mean $25/day-worth-of-traffic-pushers.