I think Shell Management's complaint equates to the same issue in the perceived lack of ISO9001 in the airline indutry too -
ISO9001 just doesn't fit into what happens to an airline either. Sure, some administrative areas can make it fit and do operate on an ISO system, but it's essentially a production or manufacturing system that can't really cope with the intricacies of airline maintenance without getting complicated, costing time (and yes, money too) that is needed to meet timelines.
In my view a good SMS is far better than an SCS, it is flexible to the type of operation and easier to maintain. An SMS can be as complicated or as simple as the operator requires.
To be honest, an SCS is just another system that depends on the indivudual working it, and the managers reponses to it. It is no better and no worse than an SMS.
This is not about a lack of an airlines/operators safety for personel, pax, property and the environment - but about the use for a reasonable method of controlling what is going on for each company, being aware of the real issues and avoiding or mitigating their effects effectively until a permanent fix can be made, if at all possible.
Maybe ICAO will make it a mandated system, but only when it been proven to work - when there's no more ships sinking, oil fires or nuclear leaks, for instance.