This is a sincere question, not pot-stirring.
Is O2 not checked for "Tested and 100%" on the A330? I do realize a gauge may show line pressure even if the valve is closed, but then testing via the mask would show that very quickly that O2 was not available? I'm not so much surprised that a valve was closed erroneously but that it made a flight with it in that position! Payne Stewart anyone?!
Of course maintenance should have some very serious questions asked, ie if they missed this, what else did they miss? But O2 seems like an item that we as flightcrew at least have a way of testing for ourselves - as well we should for such a crucial item!
From the number of outraged experts spouting off in the article, it sounds more like political axe-grinding than anything...