In my opinion, there isn't anything sneaky about it. I think having a strongly suggested standard is much better than having a mandatory certification. It places the responsibility for helmets to meet the standard on the companies that manufacture the helmets. Personally, I think it makes more sense for a manufacturer to do their own testing and ensure that it does meet (or exceed) the standards, rather than send it in for certification as it accomplishes a couple things.
Manufacturers can create and market new models more quickly and inexpensively because they are not waiting on some government agency to do the testing.
It helps manufactures to stay honest rather than be controlled by the government. If a manufacturer gets caught placing labels on helmets that do not conform to the standard, they will either get a "talking to" from the NTHSA (for help on product development to meet the standard) or get sued from consumers (the latter may be scarier for most manufacturers).
If a helmet doesn't meet the DOT Standard, then don't put the sticker on it. Companies do not have to meet the DOT standard, any other standard or certification. There are lots of helmets out there that do not meet the FMVSS 218 standard, no big deal. It's all about choice, honesty and responsibility rather than government control.
Soren