AWStats isn't detecting the correct browser version due to IE Compatibility Mode being turned on. Compatibility Mode is turned on by default when browsing Intranet websites. See settings in IE -> Tool -> Compatibility View Settings -> Display intranet sites in Compatibility View (checked by default). This causes AWStats to only see MSIE 7 vs the real browser.
Please add a switch to detect the IE Browser version by looking for the "Trident" tag in the user agent if present.
More info about the Trident tag is here: http://msdn.microsoft.com/en-us/library/ms537503.aspx
Example tags from IE 9 running on Windows 7 x64:
Regular: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)
WITH Compatibility View: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; InfoPath.3; chromeframe/29.0.1547.57)