This still begs the question as to why the minimum bid should be different for different advertisers in an auction system.Especially to apwade and stuart6mac: I'm not trying to defend Google nor attempting to discount your sense of frustration, but I'm reminded of the cliche that "we are underlings" -- and this is perhaps one of the truths when it comes to the relationship between we mere mortals and the Google Gods.
In any case, if your per click rates are going up, there are a number of reasons. The main one is certainly rooted in the supply and demand situation: the more people bidding for a given keyword (or expression), the more the price will rise. But, just as likely, there's the Google built in idea -- whether you like or agree with it or not -- of encouraging you to work on what they call your Quality Score. Nefertiti's explanations may seem (and no doubt are) difficult to understand, but, if you'll allow me to say so, she's telling you what you need to hear, even though it seems to not be what you want to be told.
Nevertheless, she's undoubtedly correct in suggesting that if you want to see your cost per click go down, your answer lies in pushing up the focus/relevancy of your keyword(s). For instance, while you may think that "book about a cat" is sufficiently specific, you have only to realize how many of its kind exist. It has to run in the hundreds or even tens of hundreds, so why should Google's favour shine upon you? You're simply one of a fair sized crowd, are you not?
Not being aware of your product or its content, to say nothing of the exact wording of your AdWord or the precise choice of keyword(s), I can't begin to suggest where the potential improvement lies. However, if I'm to be teased by your ad, my click on it needs to be triggered by a whole lot more than "a book about a cat." I need to be intrigued about connecting with a cat that talks to people, a cat that loves mice, a cat that can count up to 555, a cat that has 19 lives rather than the usual nine ones, etc., etc., ad nauseum. In other words, I want to be told by your ad that "Heh, here's something you don't know / may not be aware of / can have you laughing your head off / bursting into tears / etc., etc., ad nauseum."
In other words, you gotta be different and stand out from the crowd if your ad is to pull the way Google thinks it should. Think about this, really think about it, and then have the courage to recognize that the fault lies not with Google, but with you (and other frustrated souls) because, ahem, we are underlings!!
Such is clearly discriminatory. What cogent argument is there for the justification for such?