I'm new to this, but I think I can guess the causality in both circumstances: failure to maintain a proper course. I know in the m/v Mariner's case, they had experience in going that route (a "recreational" route, and not a formal shipping channel), but probably fell victim to a rising tide and couldn't clear the bridge. What gets me about that one, is why, when the clearance is so close on a vessel of that displacement, that they don't make use of range finders or something to more accurately assess how much room they have between the tallest point on the vessel and what they are navigating under (I'm guessing that's what the article means by "navigational instruments"?). If they did have them, and didn't use them, then they should suffer the consequences. In the case of the Costa Concordia, that one was just wanton neglect of safety and Italian bravado. For a while I thought the story would reveal that he was under the influence of something, but it wouldn't surprise me that the captain was just a "show off". I don't think we'll know all of the details of the m/v Mariner's story for a while, but in the case of the Costa Concordia, I think it's safe to bet that that captain will be behind bars for quite a while and never be allowed to captain any vessel ever again. Do I get at least 1 point?
edit: I just re-read your 2nd question- yes, "de-skill" or "deskill" is a word, and his use of it seems appropriate to me. But, as mentioned in many other SN threads, I don't think there is any substitute for basic piloting skills where the risk is so high as in these examples. That's just me thinking as a newbie with the advantage of hind-site. We'll see what the courts decide on what happens, but I think Schettino will go to jail, the other guy- perhaps not. As to whether the outcome of these proceedings result in professional maritime policy changes- for the former, God, I hope so-- for the latter, we'll just have to wait and see.