
Google = new M$
You could argue that Norton does the same thing. I made the mistake of having a page with links that used banner sized images (468x60 pixels in size). Norton users found that these links were completely removed without any warning or indication.
As an aside, some sites deliberately use 404 error pages as an alternative to Mod Rewrite (i.e. to parse the url and deliver url-specific content)
The comparisons between what the ISP did and Google are slight- but the fact that they both insert their own content to redirect you elsewhere is absolutely shocking (I can forgive Norton - at least they didnt replace the links with links to their own site!)