Also, I have to doubt those numbers. Kids aren't honest about their pot use. It's more rampant than you think. And the statement that pot use leads to other drug use is also true, for a whole variety of reasons stated by others on this thread, not because it makes you crave other drugs.
It does make you more open minded towards them, plus they are there available among the pot user's peer group, and the peer pressure to try them is always there. Many drug fatalities occur from first time use of meth, the next socially acceptable drug up from pot. Smoke some pot, do a few navel shots, and their goes their inhibitions.
"Just imagine what legal TV ads will do."
It doesn't have to be advertised.