Small Car Safety - Is that Relative?

Forbes.com lists the safest small cars of 2010, but some of them are receiving a couple of "acceptable" ratings, not good. What exactly does "acceptable" mean? Surprisingly, the Smart fortwo has made the list, in the category of the rear test rating. Seeing those vehicles on the street, makes me wonder just want was used to check that out? Other Smart or Hummer? http://tinyurl.com/safetyonforbes