A little more historical/legal background:
NJ's AWB was pretty much the first in the nation. As such, the language was experimental, but it did serve as the model for the Federal AWB that followed in short order.
The language bans certain firearms (through a mechanism of mandatory registration and a closed registry) in three ways: by name (Hence the explicit prohibition of "AR-15", "CAR-15", etc), by certain evil feature and/or a count of evil features, and by what they'd hoped would be the catchall, the "substantially similar" language.
The "substantially similiar" language was struck down as being unconstitutionally vague in a lawsuit faught by famous NJ gunlawyer, Evan Nappen. The essence of the ruling was that since a post ban gun didn't have the same evil features as a banned gun (ie: a bayo mount, etc) it couldn't function the same way, or in the same capacity, and therefore, was NOT "substantially similar". The state AG issued the "Name and evil feature" clarifying statement, so as to close off the second prong of the argument from being pursued in subsequent litigation which held that since an ordinary man couldn't determine for himself whether he was in violation or not, the whole thing ought to be thrown out.
If you follow the progression of state AWBs, you'll see that the statutory language was adapted after observing the practical effects in NJ, so as to include more scary looking guns, and not present the "loopholes" that exist in the NJ statutes.
The way in which this is achieved is instructive. Typically, fewer evil features are allowed, especially detachable mags and pistol grips, "similarity" language is beefed up to be more inclusive, and in some cases, the determination of what is and isn't an evil assault weapon is delegated to a state agency, typically the AG, who is given wide latitude in the matter.
