They need to show that there's some Code that could be made enforceable by legislation. It's part of the bigger plan to lever the ACS into the same role that the law societies or the AMA enjoy.
I also just looked at the website, and all of the membership levels look like rankings in a guild system to me. Spend your time, pay more money, rise in ranks. Protectionism at its finest, and even though I'm heavily a software developer, I'm still against this burden.
Basically software liability is just rolled up into the relevant market. Writing facebook games? It doesn't really matter to society if you get it a bit wrong. Writing pacemaker software? Then you're governed by medical device regulations.
Software's application to problems are so varied, so wide, that it's insensible to apply a single liability scheme to it.
The wide range of software that can be written precludes a standard measure of risk and liability, hence it eliminates the need for an (software) industry wide accreditation body.
Plus I've always found smaller more local meetups to be a better way of interacting with a specific development community.