As you know you can choose to display ads on the so called content-network. The content network is made up by websites that have signed up with the adsense program. The name (content-network) does not fit very well. Some of the sites do not have any content at all. With other sites it's blatantly obvious that many pages were designed not to be usefull to anyone but simply to hold a couple of banners.
What is suprising is that the adwords program does not allow advertisers to filter out such websites. Google does not seem too inclined to do filter them out themselves. As a result, those who choose to advertise on the content network will have their ads displayed on all manner of sites, even the ones they do not want to advertise on.
Google recognizes that there is a quality issue, that is why they charge a lower rate for the click throughs recieved from content network sites, but often that is not enough becuase some low quality sites still manage to produce a large number of click throughs. Besides which the lower payouts effect everyone not just the bad sites.
At Rad Inks we studied a random sample of 1000 clickthroughs and found that 542 of them originated from the same website - a site that we do not want our ads to appear on. The only option is not to use the content network at all, but then we do not get the desired amounts of traffic.
Now to get back to the "Pick the exact sites where your AdWords ads appear" statement. This just means that you will soon have the option of using CPM advertising instead of CPC advertising. Since CPM ads will run in comptetition with CPC advertising, chances are this will not lower your advertising budget.
Unless google allows some really low (I am talking about