Comment by t.broyer:This page has last been updated on Feb 4th of 2010, nearly 2 years ago; and it starts with "IE8 was recently released", so it's quite clear that it's outdated.
See http://code.google.com/webtoolkit/release-notes.html#Release_Notes_1_7_0 which says: "This release adds explicit support for Internet Explorer 8"
For more information: http://code.google.com/p/google-web-toolkit/wiki/IE8Support -- http://groups.google.com/group/Google-Web-Toolkit-Contributors