NEC3 contracts do not refer to CDM - so what?

A few times now I've had discussions with legal advisors asking why NEC contracts do not refer to certain UK statutes, CDM in particular. I can't really level with this apparent craving to refer to certain UK statutes in contracts. Why should a contract refer to any UK statute, it's not exactly an opt-in, opt-out set of rules? The exception that I can see are those statutes that do need complimentary provisions such as provided through Y(UK)2 or those that are a sort of opt-in, such as provided for in Y(UK)3.

I refer to an article printed in ribajournal.com linked below (to scroll down touch on the red vertical line, which took me a while to discover!!):

http://www.ribajournal.com/index.php/feature/article/why_make_life_more_complicated/

Anyway, in there it states "... the PSC does not contain specific provisions requiring the consultant to comply with the CDM Regulations. Clients therefore generally tend to insert a Z-clause to this effect (even though a consultant would be required to comply regardless of whether or not a provision had been included)..."

So, this looks like legal advice to me, you have to comply with UK statute. If anyone thinks a single sentence in a contract actually makes people design/build safer I think they are wrong. So can someone please tell me why on earth we can justify padding out contract terms with unnecessary references to UK statute that apply anyway?

Rob