If I recall correctly, that was not the case. However, we did have /anon/ so horribly under-moderated that nobody cared much. Oh, and /oat/ had gotten really lewd anyways, so the line was rather blurred as to what exactly constituted 'explicit'. We determined it to actually be genitalia, essentially.
Left some really lewd stuff, though.
It's just a law thing. Even 4chan does it, though there's is for specific boards, I believe.