Is Google's Adsense more effective (higher CPC) on some sites than others?

Google certainly has different CPC for different sites.... the sites which are old and people like spending their time on it and the ones which generate more traffic has much higher CPC

Yes and no. The rough answer is yes but it doesn't depend only on the site, more on the blocks.
You could even get a smaller $ for your clicks if you have too many blocks on the ONE page, the money seem to ge "diluted".
If you have just the one block and they click on that, it's more money that if you have a few..
But yeah, there are other scenarios where you might be a placement ad and they are all fighting to get on it, then you'd get more money for your ad space.

Absolutely, google uses several different algorithms to calculate the CPC for different keyword/site combinations. The more popular your site (popular being highly ranked by google), and the more targeted your site content the more targeted the adsense ad will be and the higher the cpc.

There are also a number of vendors on the web who sell 'high value' keyword lists. I have not used these services and have heard varied reports on their value so buyer beware.

Alot of it depends on how well designed and done your web site is. Title, and description and keywords are still important. as is the relevancy of those to the text on your main page in particular.

yes , i like it very much

It depends on the content of your blog, and the advertiser competition for certain keywords.
I have blogs that some clicks pay me 3 cents a click and have some blogs that when people click on adsense I make over $3.00 a click.
No matter what the content is getting a lot of traffic and your ad placement is the key to making adsense money.