It's one thing to explore, it's another to be so frustrated with not being able to find whatever FedEx item you are supposed to collect that you quit the game. The fact remains that the vast majority of people don't finish the games they buy.
This is just silly. Quest compass prevents people from thinking. Decent map + regular compass + quest log + clear hints where the person/item/whatever is should be enough for everyone who can process information they receive. Even if the player is lazy there probably will be 947383 walkthroughs on the web which (s)he can use...
Oh, wait 'using of google' isn't a popular skill these days.
The lack of such helpers as a quest compass rewards patience and persistence. When you play the game for the 2nd, 3rd or 15th time you'll remember much more of the game layout when you're not guided. Some quests would be completely ruined if the game just pointed you to the next person you have to find (e.g. mystery quests where you have to look for clues). Of course if it's (lack of compass) not accompanied by decent quest info then you're screwed, but it's the devs job to write the dialogue and quest hints so you won't be. And this is how we get to the second point:
you don't want it? Mod it out.
I don't pay my hard-earned money for the game to get a product with defects (from my point of view) that I would have to fix myself. This is the creators job for Christ sake. How many times did you buy a broken freezer just to tinker in it a bit before it was freezing stuff properly? I want my freezer to freeze and games to entertain me without my help.
The fact remains that the vast majority of people don't finish the games they buy.
Who gives a damn? They paid for it, didn't they? Heck, people are buying next-gen consoles just to smash them on a youtube video. It's a free world.
(Arcanum is a good example of a detailed log available)
In Arcanum was sometimes pissing me off that notes were sometimes a bit vague (quest notes) and they weren't categorized (rumors). Scrolling through 50 pgs of writing looking for the stuff you heard long ago is quite tiring.
A perfect log should be like in Arcanum + the possibility of your own notes (if you could make notes on the map it would be even better) + viewable under different categories like: specific regions/people/types of rumor etc. which could be a bit unrealistic in Arcanum, but should be completely OK with a PipBoy thus making a quest compass obsolete.
Exploding cars: Radiation may come from some kind of deformed idea of a 'dirt bomb'. We have some radioactive stuff in the car, it blows up and spreads the radiation around. As you stated fusion doesn't produce radiation so I guess this has no scientific basis, but that could be the idea the devs had.
Finally
Thanks for a great preview Mr. Burke (one of 3-4 good ones from around 40 I read) and answering our questions.
I got one more

Was the TPP camera following the back of a player ('classic TPP view') or could you just fix it somewhere and scroll with mouse/KB/pad ('RTS like' which would be better and more iso-like for 'purists', If you could rotate it and zoom it would be almost perfect).