One could always click "uninstall" after downloading.
I suppose that it is really unnecessary to make it required. My reasoning was just that it would allow for an accurate list of all users whom are using the modification which would be useful both for accurate install counts and notification in the event of security flaws. With AJAX forcing the click of the "install" button wouldn't be that big of a deal.
But, as I said, I definitely see your viewpoint on the subject. It is far more userfriendly to not require it.
And in response to Shazz and Princeton:
Perhaps I was not entirely clear in my post. My suggestion was to require the clicking of the Install button before the download link was made available. All "installed" hacks would have their download links available, if a user were to download a hack more than once the install count would not go up only the download count. (vbhackers.com has this system active if you are unclear and care enough to check it out lol)