Crystal.CarvI agree -- there was a time when skis were much more simple and I think the pole plant was needed to help do a type of jump turn. People still use them today obviously.. even half-pipe riders and racers who never do plants. Personally I stopped using them many years ago. It was a great liberation.
Double post but this comment sparked my interest.
Even with today's ski technology people still do jump turns. You usually end up doing jump turns when you're trying to shred something quite steep (40 degrees +) and something that is most likely narrow as well.
Also it's worth noting that you don't need poles to do jump turns. Try it, I promise they will still be just as easy to do as they were with poles.
So it's not really the jump turn its self that induces the use of poles, it's the terrain that induces it. When you're trying to shred something steep and gnarly, the last thing you want to do is fall. What is the best way to ensure you don't fall? Having the best technique possible. This is where the poles come into play. The use of poles really highlights certain movements that are associated with good technical skiing, those being things such as standing all the way up in between turns and having your upper body (and hands!!) driving down the hill. The best way to ensure your upper body is driving down the hill is to pole plant, and the best way to make sure you are fully standing up between turns is to try and pole plant. Poles also assist you in making it easier to find some rhythm in tough places (weird moguls, crud, chop) and when you're in a tough spot, your pole plant will actually show you where your next turning 'axis' will be.
Pole plants are good kids. Do them.