Thats not surprising in the least bit, In fact if you're really paranoid you can assume most of the signing authorities have given up some of their private keys....
I might be completely off base and confusing certificates and keys here, though...
Gibson Research Corporation created a page that shows the real signature for some common websites (and lets you check any site you want). You can then connect to them and view the signature in your browser and compare them. This is what you would have to do to know if you were being MITMed with a "real" certificate.
Here's a current list of Moz's http://www.mozilla.org/projects/security/certs/included/