Sam:
That was the case for a long time, but Evan Nappen, esqu, took them on in court, on the basis that the "functionally equivalent" language was unconstitutionally vague with respect to post-ban configurations.
The court agreed, (shocking, actually) and the general concensus is that post ban AR types not named "AR-15" are legal to purchase/own/etc. You'll even see them in gunshop racks these days.
The decision noted that without the bayo mount, the function had indeed changed, and thus it was no longer "functionally equivalent".
A letter from the state AG clarified that "assault weapons" are those listed by name, or any that exceeds the evil feature count.
I'd say that the most problematic AWB is probably California's, although CT, MA and a few other states have strewn some legal landmines around as well.
My take on it is that CA took note of the failure of NJ's AWB, and corrected the language on it, to achieve their evil ends.