Brakes are always more powerful...and I really don't know why you wouldn't just grab neutral.
That being said, it does throw you when you experience it and you aren't thinking completely clearly. I've never had it in a car, and am a little skeptical that it happens as frequently as people indicate, but I had it happen to me a couple of times on a dirtbike when I was younger.
The throttle cable would just get stuck (incidentally, this normally occurred when I was heading towards a tree with lots of low hanging branches and not a lot of manouvering room) - it does throw you a bit. But I remember just reefing on the throttle backwards (which generally didn't work), so I'd grab the clutch and kill the bike.
But grabbing neutral is not your first thought, rather its, "hey, why am I not slowing down, am I off the throttle?" followed quickly by "wow, that's a really big tree, this could really hurt."