That's the point - a blog that uses jetpack doesn't ask me if it can share my e-mail address with wordpress.com - it just does, and I would say no if it did ask me because I don't want that to happen, I would rather not subscribe to the blog than have my e-mail shared.
And a lot of the sites have privacy policies stating they don't share my e-mail address, yet if they enable jetpack that is exactly what they are doing probably without even thinking about it.
Since the plugin itself doesn't inform me the e-mail address is going to be shared with a third party, any blog with a privacy policy stating they don't share my e-mail address is lying to me (unintentionally but still) if they enable jetpack and my e-mail gets shared with a third party.