Well, to be sure, Jews were folding their hands in this manner even before the time of Jesus. Thus, it is likely that Jesus, too, prayed in this manner, reaffirming that it is, in fact, pleasing to God. So us Catholics picked up this traditional pose from our Jewish roots. Further evidence of this is the Judaic custom of "giving tzedakah." Tzedakah translates to be charity or almsgiving, and there is a Jewish saying that advises one to "give tzedakah with both hands." In other words, give generously, folks! :)
The same goes for our prayers of thanksgiving and supplication to God. We pray with both hands, our fingers pointed upwards to the heavens. To pray in this manner helps us focus better on what we are really saying.
However, it's unlikely you'll find a Jew praying in this manner anymore. Why? During the Middle Ages, Christian antisemitism was unfortunately alive and well. As a result, many Christians attacked and persecuted their Jewish neighbors in barbaric and cruel ways. In response, rabbis ordered their people to discard many of the similarities they held with Christians... steepled hands during prayer being one of them. Jews, understandably, wanted no parts of the Christian culture that was ruthlessly sabotaging their existence. They sought to sever any relation - even percieved - from the oppressive group that persecuted them. The effects are still seen today and is why we no longer see Jews pray in this manner.
However, those are, in fact, our roots. For as ugly and sinful as those roots are, it is good to be aware of them. I think, in His Wisdom, God was smart to gift us the tradition of folded hands. To keep them occupied in such a manner frees them from poking your sister, playing with your hair, or flipping through the pages of the missal at Mass. The good sisters were wise to continue passing along this tradition to ensure we were well-behaved in Church! Ha ha.
Anyway, I hope that answers your question, Lori! That is, in fact, why we fold our hands today. It's becoming a lost art. It's not seen as "important" or "progressive" anymore. Much like the veil, it's seen as an archaic gesture unnecessary in the modern world. We couldn't be any further from the truth. Let's bring back folded hands! :) Those nuns were on to something!