Why do advertisers want to bid more in adnetworks

[UrAdGinny]

Why do advertisers want to bid more in the adnetworks ?

If I can get my ad running at say $0.2 for CPC, then why I see higher bids in the adnetwork.

Why would the advertisers want to pay more?

Is there a way where the advertiser pays at a rate for which he has bid and not more nor less than his bid ?. I Am talking about taking control over his ad spend.

[SlimKim]

they want to up the price in order to get more volume ... if you and they bid the same amount and they were profitable, you just took half their volume and they are willing to pay more to get it back ... that's my take

Hope it heps,
Slim