Bloody shins do not equal good form universally; it is really only true for those unidviduals who are "built to pull." This is from Tate's "Dead Zone" article. It is a list of ten common mistakes in training the deadlift.
Mistake #6: Keeping the shins too close to the bar
I'm not too sure where this started but I have a pretty good idea. Many times the taller, thinner lifters are the best pullers and they do start with the bar very close to their shins. But if you look at them from the sides they still have their shoulders behind the bar when they pull. This is just not possible to achieve with a thicker lifter.
If a thicker lifter with a large amount of body mass ? be it muscle or fat ? were to line the bar up with his shins, you'd see he would have an impossible time getting the shoulders behind the bar. Remember you need to pull the bar back toward you, not out and away from you. So what I believe happens is many lifters look to those who have great deadlifts to see how they pull, then try to do the same themselves. What they need to do is look to those who are built the same way they are and have great deadlifts and follow their lead.