Pork Chop: You may have one legal standard, but that doesn't mean you can't buy a helmet that meets it and meets SNELL or some other higher standard as well.
To everyone arguing all standards are the same, i promise you they are not, and they matter lol As an engineer i deal with them daily.
The examples Dave has pointed out are fairly clear. Its like saying "I can hit you in the head with my hand, or i can hit you with this metal pipe?" Both will hurt, but one hurts more.
Helmets held to a higher standard code let LESS FORCE through to the rider on impact. Therefore they are 'better' helmets. This is typical of national systems, if the government has lower standards it allows more companies to produce products and thus higher revenue for everyone, so holding a very high national standard makes little sense even though in this case it would save lives, or at least time spend in the hospital.
EDIT: Charles, I read that article and from what i took away was this
1. The article states that SNELL helmets ARE designed better, to a higher standard
2. They say that in any crash that would destroy a DOT helmet would likely kill you by injuries sustained through the rest of the body anyway
3. SNELL tests are more rigorous, and hold 'unrealisticly high standards" Such as repeatitive impact with smaller objects.
4. The article states a 200G threshold is safe, and all numbers under 200G are essentially equal (ie- 5G impacts are same as 150G impacts since they are both under the threshold)
From those main points i would STILL rather have a SNELL rated helmet, i would rather have a 5G impact then a 150G rated impact any day, anyone who says otherwise is free to come over and i'll show you the difference
Also - DOT standards are focused on flat impacts, where SNELL holds higher standards for irregular object impacts. So when you fall off your bike and your head swipes that road barrier pole, you'd be better off in a SNELL, or if your in a wreck and your head hits that curb, or rock on the side of the road, SNELL would be safer.
I also don't feel comfortable saying "Well if my helmet fails my body will be effed anyway so why bother!?" because i wear proper gear, or excessive gear to prevent that, i want my helmet to still be functioning.
Basically SNELL seems like it tests for the 'odd case' that 5% chance, DOT ignores it and says it won't happen. Well it does, every once in a while and if I happen to be that 'odd case' i'd like to still be alive.