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.
*Drinks coffee*
Just out of curiosity, how would any service perform a double-opt in without sending the recipient address an email first? Sending that email for verification is not the same as sharing an email address or using it for nefarious purposes.
If you don't want your email out there (and that's fine and I 100% support your decision) then don't share it with anyone. But please do not ascribe bad intentions for double-opt in. Double-opt in is a good thing and if the user doesn't confirm then then address is not used.
*Finishes 2nd cup, gets more coffee*
;)
It's the weekend so let's wait for a reply from someone from Jetpack for that statement. People even volunteers take the weekend off sometimes.