At least something will be written down
I'm as cynical about the business ethics of large companies as the next person (provided the next person is fairly cynical). But at least this represents a tiny step forward - something will be written down, and it will provide some means to hold these companies feet to the fire. Of course it has no legal force, but public embarrassment is quite a strong force when applies properly. If the code is worded in such a way as to allow lots of wiggle room to the signatories, that still provides a wedge with which to push for better behaviour.
If the large businesses gather under such a code of conduct, other businesses may follow, and that will help tell us where a given business stands. If enough businesses stand behind one code of conduct, it might even give those companies negotiating strength against the regimes in question (though I doubt it would be used that way).
As things are, companies can wiggle and change their direction as they see fit. At least this will tie them down a little bit. It can't be worse than things are now.