Why do you jump to the assumption that they're malicious then?
Put a few more branding elements into your page design, so that visitors to their site will understand that they're redirecting your data. Then take advantage of the extra publicity that they're giving you.
Having a duplicate site would do a lot of damage to my Google search rankings.
Not sure if he's stripping it, but serving a 'canonical' meta tag would solve that if he's not,