This difference may be caused by some of the factors stated below.
2. Use of Adblocker by Visitors:
Secondly, some of your visitors access your blog with adblockers enabled on their browser. The primary aim of adblocker is to disable ads not to show on a website when accessing it. So when a visitor visits your website with adblocker enabled on his browser your Google ads wont be displayed to such visitor and hence Google adsense won't credit it as a pageview.
3. Spam Visits:
Stats may also differ because adsense filter out many visit that it thinks they are spam.
There are also some other reasons while both stats will differ but this are the 3 major reasons. If you have other ideas you can share with us through your comments.