I used the "rat trap" style straps when I was younger. When I started cycling again, I was not keen on investing in new shoes just to ride a bike, since a lot of my riding consists of grocery runs and getting out to places where I get off the bike and explore.
So, I put BMX pedals and "HoldFast" velcro straps on my touring bike:
There are a number of various velcro arrangements. Even though the velcro might release before your ankle breaks, I didn't get to test that theory.
Last year, the LBS had a sale on Shimano mountain bike shoes, which work well enough for walking around off the bike, and are actually pretty decent for "I think I'll have a look-see down that ravine for a bit" shoes.
So far, I've had four "didn't unclip before stopping" falls - two of them on one century ride. I did 100 miles across southern New Jersey and came out with matching elbows:
(the ride was great - http://www.mapmyride.com/workout/987888953 - lots of headwind coming into the Jersey shore )
That said, there have been several instances where the better mechanical coupling to the pedals has allowed me to maneuver the bike in situations where I might have otherwise come off the pedals.
But, yeah, like you, I spent a lot of time wondering about the relatively risk of clipless pedals, and have come to the conclusion that the better bike handling - you aren't going to get easily bumped off the pedals - on balance reduces the risk of injury overall.