There is some argument to be made that the lesser DOT standards may be sufficient, and in many cases, better than the more stringent European standards. The euro standards are very specific (two heavy ball drops on the exact same place on the helmet or something like that), which are not representative of accidents and likely result in having helmets that are far more rigid than they probably need to be for 9/10 accidents. Having something that is too rigid is like having a head on collision between two 1970's cadillacs... the car's (helmet) might come out looking better when they are more rigid, but your body (brain) takes more of the whiplash as a result.