question in regards to CPC

i have been tracking my channels

[dailypress]

I have created seperate channels for my website and track my earning several times a day. This website consists of a few pages and each page has an individual channel:

I noticed some clicks generate over $1 and some as low as 2 cents! How does that work?
I thought advertisers bid for keywords and google displays ads depending on the content.

i.e. If the keywords for a page is X and Y which is worth $1 CPC each, how do some 2 cent ads show up?

[thegreatpretender]

One thing, google serves mix ads with different payout on every pages. And a lot of more factors that come into play as far as payout is concern.