Google Denies Preferential Treatment for Own PPC Ads

The discussion about Google keeping its own ads at the top of their PPC over at Search Engine Watch has gotten some interesting comments.
The AdWordsRep discussed it with his people and replied that this was not happening. But it seems it is not just something I have noticed, from the additional posts that this thread has received.
Would be interested in anyone else who has any experience in this area to share with us.