I'm decently sure the answer is yes, but my Mom and I disagree, so here goes:
We recently sent out our STD's via Paperlesspost.com. The STD's had the standard info on them: Save the date! Our names are getting married. Chicago, IL. Date. Direction to wedding web site. Formal invitation to follow.
Paperless Post allows people to send a message to us. Most messages are lovely congratulations and whatnot. A couple of people have actually RSVP'd no by message. To be clear, the STD didn't ask for an answer, they just volunteered the info. I assume that we still need to send them all invitations, even though they RSVP'd no, right?