The AJAX Helper is a tool to help with the implementation of AJAX on the site. Its what allows for some of the advanced web 2.0 type functionality and it's used on a wide variety of constituent facing pages. AWstats is picking up on it as a separate page but it's actually just a helper as it's name suggests.   It is part of the back end systems, but it will show up in AWStats quite a bit for all of our clients using AWStats.  There is no way to explicitly restrict the AjaxHelper from AWstats.

In the same place where you have the link to AWStats, you can go to the raw web logs. You can download a day's worth of the log and search for /site/AjaxHelper. You can find lines like this: - - [27/Jan/2010:08:30:20 -0600] "POST /site/AjaxHelper?JServSessionIdr004=txb8xzenb1.app9b HTTP/1.1" 200 12321 "" "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/532.0 (KHTML, like Gecko) Chrome/ Safari/532.0"
This will show where the AjaxHelper was called from. In this case, it was a donation form. TeamRaiser also uses the AjaxHelper often. This should let you see where this is being called from if you're interested.