Humblebumble
The guy who wrote the ListeningToKatrina blog that Chinkapin posted on page 1 discussed that kind of thing.
The big mistake a lot of people make is seeing the BOB as the answer. it's not - it's part of the answer though.
Granted, a BOB is no good if you're in such a blind panic that you burn in a house fire... but if your fire drill doesn't involve grabbing the bag under/near your bed, why not?
A BOB could just be insurance documents, photographic proof of belongings (all on a data stick), proof of ID (birth certs and the likes) and some clothes.
No need to waste time trying grab clothes and a few documents on the way out (you probably won't have time to do either if there's a fire). Grab the bag, grab the kids (assuming there are any) and get out starkers - once outside get the spare clothes out of the BOB and get dressed in the street, alive and well. All safe in the knowledge that you can prove your insurance, that you had the TV the insurance doesn't want to pay for and so on.
I think the right way to see a BOB, at very least, is a container for a few essentials and assuming you won't ever get back into the house (which is what you should be assuming if preparing for a house fire) the things you'll need to get your life back on track and also whatever you can't replace if you're leaving a house/flat that's going to burn completely to the ground. (I'm thinking about digital copies of photographs and the likes here - maybe even the originals in a folder/album of some sort - display copies in frames).
Prawnster
It sounds a bit like you're already seeing the point.
I think of a BOB, first and foremost as one of two things... (In fact, I'm working towards keeping two separate bags, one for each)
1> Grab-and-go bag.
"Let's go camping/to grandma's/to Paris for the weekend."
No need to mess around looking for what you need - it's all in a bag ready to go. No missed opportunities for not being ready.
That's where I started after taking several last-minute trips that were delayed by not knowing where the things I needed were. That lead onto...
2> An actual Bug-Out-Bag.
In this case it's smoke alarm goes off and I don't want to stop for anything - I'm getting out NOW.
It's got clothes I'll need to put on once I'm out (I'm not stopping for clothes).
Essentially it's "if the house burns to the ground and I've got one bag to carry things I absolutely don't want to/can't do with out - what's going in?"
You've got no chance, after the fact, to go back in and get your passport, birth certificate, medical stuff, car keys, money, photos of dearly departed and so on - might as well have them all ready to go at a moment's notice, and since there's a chance you're going out a window, not down the stairs, it needs to be in the bedroom with you.
Once you've got that level of preparation for something far more likely to happen than major natural disasters (and probably more likely to kill you) - you're pretty much prepared for anything. (Not that those anythings are all that likely, but it doesn't hurt to be ready.)
I'm sure Wolfie can be a bit more succinct than that - but the "why" of preparedness (in the non-nutjob use of the word) is pretty complicated.
Maybe "If there's a fire I don't want the kids to burn or to be homeless/jobless/carless/mementoless afterwards." (Probably a couple of made up words in there).