Did a little research on Google and it sounds interesting. Looks like the history is that they were come up with sometime in the late 60s and was approved for use. Because they are a heavier pin, apparently they react quite differently, as in less scatter and pins flying around so it's a challenge to have a higher scoring game.
Check up on "Lumberjack" bowling tournaments! Apparently it causes quite a challenge since accuracy becomes more critical when you don't have a lot of scatter.