Shipps, please explain how elbows can block a turn (which happens primarily from the feet)?
If anything, a close elbow might block the upper body from rotating into the turn (which would be a good thing).
To your point above, it doesn't matter where the turn starts. It is about maintaining balance when skiing natural uneven terrain. If your elbows are in close to your body you can not maintain your balance and position over your skis as easily. Think of it this way, ballet dancers, tight rope walkers, tennis players all keep their arms wide to maintain an athletic stance and keep their balance. Same thing applies to skiing. If your elbows are in close, instead of held high, a skier is much more prone to dropping a hand out of their line of vision and rotating the upper body against the turn and up the hill to some degree ( when being bumped around).
It may be better to say that arms held in close slow down the initiation of a corrective move that will help you maintain balance and fore/aft position. This means you are coming from a reactive position instead of a pro-active position when maintaining your balance on difficult terrain. This is because close-in elbows require that you move them out wide to maintain balance (reactive) before you can initiate corrective action (proactive if you don't have to move your arms). When moving at speed, a reactive move generally makes you arrive late at the corrective action, be it a turn, hop, jump, or whatever it may take to stay in balance, and flowing down the hill. Arriving late results in a loss of control for most skiers. I am just saying that keeping your arms wide, elbows high, and palms facing each other is one thing you can do to improve your skiing.
Remember, I am talking about skiing in challenging terrain. Cruddy natural moguls, natural moguls in general, tracked powder on steeps, general all-mountain skiing, etc.
For me, Turkey-on-a-tray is old school and hugging-a-large-beach-ball at chest level is new school.