nomis5 - 10:22 am on Jul 9, 2012 (gmt 0)
The full sentence reads
It’s a myth that filtering ads can prevent ‘low-paying ads’ from appearing, so as always, we recommend blocking only those ads that you feel are unsuitable for your users.
That is believeable. If you believe that "loose fat" ads or similar are not suited to your site then G is recommending that you block them.
For sure, those type of ads are generating income for G and by implication, for some webmasters.
I understand the full sentence to be saying something along the lines of in general G will place the highest (in their experience) paying ads on your site. Only block them if you believe they are not performing on your site.