There's a difference between meeting standards (AKA: minimums) and exceeding them. Personally, I'm not going to trust my brain's well being to a cheap helmet I picked up for $100 brand new because it had sweet graphics and a SNELL rating. I'll pay for quality because I would like to continue to survive as long as possible.
Yes, they each have their own rating system, and I do agree that I'd only put quality on my dome but don't plenty of people use Snell only systems overseas??? Meh; I only use Shoei anyway...DOT/Snell iirc.