I don't think we have many of the nasty ones near the US, which would explain why we don't hear much about them. I'll bet in Australia they hear plenty about deaths by jelly. I'm pretty sure they have to close down beaches because of the risk, mate.
I found this vid trying to find one about how jellies are formed. I saw a show on the edjacational channel that showed a certain jelly that starts as a polyp stuck to a rock. as it grows, it had jellies growing out the top and a leg out the side. the new leg attaches to the rock, and breaks off the old leg. the old leg, grows jellies on top and another leg.
this vid is about box jellies. In the middle a guy talks about how they can see and they interact with others to catch fish.
It was an awesome article.. It is rightly saying that their number is increasing everyday and becoming a threat to the surfers too... As the number of deaths are also increasing because of jelly fishes.