From 1982 I took my first jump and continued skydiving until 1991...work, wife, kids!
I've heard of guys doing this very same thing, and on more than one occasion, I've seen guys walking to the plane without a chut until they realized they didn't have one on.
Did it myself once but only once!
After jumping for a long time and being to comfortable with jumping, its easy to forget your not wearing a chute. They've done this a thousand times and in their mind, its on their back but in reality its not.
This type of accident where a guy jumps without a chut is the same: A guy (usually a seasoned instructor with many jumps) goes in the plane and sends students out. Then he jumpes out after the last student only to realize his error! Opps!
Our club quickly changed its practice so no one is allowed in the plane without a chute on, including the pilot, regardless if you plan on jumping or not!
Lack of experiance, complacancy, over confidence and taking risks beyond ones ability are contributing factors that can cause death or injury! (Same goes for tree work).
I've known to many friends who have been killed in skydiving related accidents.
Once you loose fear of jumping from a plane (or climbing trees for that matter), your odds of having something bad happening to you increases!