Yeah I did about 2k cammy teleports today on my pure for 55 magic, and got atleast 6 times the abbysal teleport random and a couple others, and when ranging tzhaars I get about 1 every half an hour.
I've noticed that the lower level you are the more the randoms are. When my friend was level 3 he would get randoms every 5-20 mins.. and he was skilling. I got to level 40+ and barely got anymore randoms when I was fishing. It kinda sucked cause I like the sets you get, like mime-laderhosen, etc..
Not sure when certain changes to random events were implemented, but I know that after a certain point in time you would get less frequent randoms or more frequent randoms depending on the time spent on each random event, and if you were to fail a random event.