Read the post. 2 demerits for loud IN CAR stereo.
And the reason is perfectly reasonable. If your in car stereo is loud enough to legally be considered noise pollution outside the nearly sound proof box which most modern vehicles are, the driver has absolutely no hope of hearing audible warning signals coming from outside.
As far as the penalty for a pedestrian using an MP3 player in traffic... well death is a bit harsh, but only because of the life sentence they hand their involuntary executioner.
On bike paths, I have had any number of these twits out jogging suddenly turn onto another path right under my front wheel, without so much as a backwards glance. As far as they're concerned, the law says they have right of way and it my responsibilty as the cyclist approaching from behind to avoid them, WHATEVER they do. It may well be my responsibility, but this can be considered official notice: henceforth, if as a result of their actions, I am given the choice between hitting them and a pile of rocks, I WILL choose them.
Earbuds attatched to an MP3 player are as effective as an icepick through the eardrums for creating situational deafness. Almost certainly worse actually, since music is very, very good at grabbing a listeners attention (and focus), while silence at least forces a person to pay more attention to their other senses. You only have to watch the head and hands, when the rest of them is not in motion, to see how much of these people's attention is on the music and how much is on those unimportant things like trains, busses, ambualnces and uncovered mineshafts.
Even a single earbud is potentially dangerous in a high risk environment, since it effectively deafens the wearer on that side.
As for your "well *I* can multi-task" argument... Well, If you print it on nice soft paper, I will give it the same deserving attention I give to like arguments about using cellphones, applying makup, route planning, catching up on the news, eating, etc. while driving.
The human mind can not multi-task.
What we can do with some training, and considerable practice, is delegate repetetive and rigorous rule based tasks to the same non-thinking part of the brain which takes care of walking and not shitting one's pants.
The human mind, can to a limited degree timeslice, but every extra activity requiring active conscious focus demands a certain amount of cognitive overhead (stackspace), more tasks = more overheads and greater cognitive hit each task takes. Furthermore, in the event of an emergency, when full focus is required, it takes time to let go all that "cerebral housekeeping" and focus all that scattered brainpower to go to work on the one task. A bit like real mode switching on a 286 really.