Whatever the reason - they made it extremely easy for you to completely open up your account to EVERYONE by default.
I use a pseudonym on Facebook - so don't bother looking for me unless you actually know me. Even so you might say that I keep the settings on the "most paranoid" mode. But as you can clearly see above - by default they wanted to give out all of my information short of my actual Address. (As though I would actually put it up there?)
You could actually mouse-over the old settings radio buttons & see a popup that displayed what the settings actually were.
But my point is that if you were 'in a hurry' or not willing to read through this carefully - you would find yourself utterly compromised.
I think that this happened to many people recently. It is an observable and testable fact that the majority of people just click through complicated screens in a hurry to get to what they want. With the compulsive nature of Facebook use that happened quite a lot.
Cyber-stalkers of the world rejoice and use this opportunity while it lasts! People will catch on soon enough & change their settings back - but for a little while - anyone whom might have been unavailable to you just might be wide open right now.