As it is, the default action on the "Respond" button is "Respond with Comments" and I have to click the drop down to send the response without comments.
Please Respond.
Accept | Tentative | DeclineRespond With Comments
Respond Without Comments
Do Not Send a Response
99% of the time if I'm accepting an invite I don't need to comment.
I've looked through the Preferences for Outlook and I don't see anything related to this.