They actually charge you $20 less, to accept the ads.
The ads opnly appear as the screensaver, and on the bottom of the
homescreen when you are NOT reading. During reading, there are no ads.
The Kindle PW with 3G can view and download from the Kindle Store, lookup words in Wikipedia/Big Translate and share books via Facebook/Twitter via the in-book popup, and mark your book's status on Goodreads. That is it.
Amazon is not subsidizing your generic internet browsing experience.