The main reason why Google wants your blog to have a privacy page is because the concern of privacy of your blog users. Not everyone wants to have a cookie placed on their computer which tracks their browsing behavior.
There are certain theories and conspiracies regarding the growing concern over cookie droppings. This is the reason why Google Adsense wants their publishers to be careful about any outburst from their blog readers about the cookies.

Do you know that it is mandatory to have a page on your blog dedicated to “Privacy Policy”? You should also have to mention specifically that your blog is powered by Adsense ads and also inform your blog readers that the cookie is dropped on their PC when they visit your blog? Earning money from blog is one thing but protecting your users interest is one more thing.
Google is one of the most trusted companies on the Internet. So having a privacy policy page with details regarding Adsense and cookie is not a big deal after all. So how would you create a detailed page with all the info that Google wants to have you on that page?
Note: Google adsense can ban you as a publisher if you do not have a privacy policy on your blog or site.
It is quite easy with this wonderful plugin called as: Privacy Policy Plugin for WordPress. This is the same plugin I used on more than 100 of my proxy sites few months back. It is quite compatible with what Google demands out of your Privacy policy page.
You can also try this alternative plugin called as: Easy Privacy Policy
Both the plugins are quite easy to use, you just need to install, activate and click few buttons before you have your own Google Adsense Privacy policy page.
If you are yet to Apply for Adsense and get Approved then you should be aware of the Privacy policy and make sure you don’t break any rules for a happy blogging experience.
This is the official Google Adsense page mentioning about the privacy Policy Update for all Adsense publishers: https://www.google.com/support/adsense/bin/answer.py?hl=en&answer=100557
Related posts for You:
Hey, this is Kamal and I operate the NPXP network of websites. I am a blogger as well as a freelancer.
Using such plugins may fool google but one will not be able to fool the readers.
I mean if a reader visits(by chance) your privacy policy page and sees that it has been created by a bot, they might see the unprofessionalism and might just leave your blog.
So, I prefer writing all my messages and posts on my own rather than using bots.
It is a privacy policy generator which is in compliance with Adsense. So you need not worry about duplication or anything such Karan
Does Google penalize the amount you make per click if you do not have a privacy policy?
Without it your Adsense account is deemed to be banned sooner or later!
Yes the privacy policy is a big requirement if you are an adsense publisher, specially for the new dart cookie,