Why is that?

It's called a coincidence. See what Google's representative, AdSense Advisor said above:

I would be shocked if a single one of you were seeing any impressions whatsoever from Google certified ad networks yet. We're rolling this out slowly. Very slowly.

Jorge egglezias, ASA--Google's rep here--said earlier in this thread that "I would be shocked if a single one of you were seeing any impressions whatsoever from Google certified ad networks yet. We're rolling this out slowly. Very slowly." So it's likely that any increase (or decrease) in your eCPM is due to other factors.

it's getting more and more difficult to work out what is effecting your eCPM and CTR these days, because there are so many variables of which we know nothing about.

for weeks we thought that certified-ad networks might be affecting it, but then we're told we're not even getting any impressions. but it's been out for ages. so when will it come into play?

then we think that interest based-ads might be affecting it, but there was confusion about that too, whether we could turn them off or not. so we don't really know if people are seeing them either.

and then we get to set our font families, which still seem to change regardless. and the same with the font sizes. we never seem to have a problem with the text colours changing.

the only things that we can be 100% sure about are these: the text colours, ad size and ad positioning.

but our earnings are being increasingly effected by all these other things of which we have no control over. we don't even have any proper information as to whether they're running or not -- something that ASA has just confirmed for us above. maybe it's effecting our earnings and maybe it's not, who knows. google gives us the option of turning them off, so we give it a try, only to get told it's a waste of time.

if adsense wants to help us out then they should be a bit more open about which parts of their program are currently running and which are not, so that we can test properly.

I don't care how fast or slowly they roll this out. Looking at the list of approved ad networks is enough to convince me to block them all.

The number of networks on the apparently changes pretty often, too much bother to keep track of who is coming and/or going.

At least one of the networks approached me directly in the past and I turned them down. Why would I want to let them in the back door?

If adsense wants to help us out then they should be a bit more open about which parts of their program are currently running and which are not, so that we can test properly.

See [en.wikipedia.org...]

Nothing worse than testing a system to only determine that there are unknown and unseen variables (changes) affecting your test.

Accurate conclusions are then impossible and speculation ensues.

In the ad review center, it will tell you if your placement ads are from a 3rd party (Third-party Ad Sample [?]).

I am serving some for paypal and the pay is outstanding.