I want to add my voice also as being unhappy with this change to set the 'Send Invite To Group' default to 'Checked'.
In my case I was creating two place holder calendar entries that got sent to my group inadvertently which is causing a bit of confusion and embarrassment on my part. I have created temporary entries many times in the past without sending out notifications, so the change caught me by surprise. At first I thought it was my fault until I saw it in the change log.
As for forgetting to sent out notifications, that is easily corrected by editing the event and checking Send Invite to Group, where as forgetting to uncheck the box is not easily corrected.