How would that work? The AVG robot probably only fetches the page's URL. By the time you serve up a JavaScript, you've already lost the ability to redirect the robot.
Also, once enough people start redirecting the AVG robot to the AVG website, they'll just update the robot to ignore those redirects. It's antivirus software so it gets updated very often.
I guess it could be done using some combination of first placing into every HTTP header: "Refresh: 2;URL=htpp://www.grisoft.com/", which would then allow a piece of Javascript on the web page up to 2 seconds to figure out if the visitor is a real browser (maybe even including some DOM checks too), and then acting accordingly (ie: sending the user to a page without the redirect header). If AVG's http fetcher doesn't execute the Javascript or fails to pass the browser test, then it gets redirected back to AVG's site because of the HTTP header.
Convoluted? Yes. Will it work? It should, unless AVG decides to implement a full Javascript engine and DOM stack in their http fetcher. Also, the initial re-direct doesn't have to go to Grisoft, it could go each time to a randomly selected site from a list of their competitors <evil grin>.
I think AVG is really playing with fire, it's really only a matter of time before things like this start popping up as defense mechanisms.
Presumably, AVG loads extra resources like images, CSS, iframes, <object>s etc. from your page. (if it didn't, it wouldn't be very good at finding malware, and be really easy to detect)
Also, once enough people start redirecting the AVG robot to the AVG website, they'll just update the robot to ignore those redirects. It's antivirus software so it gets updated very often.