What does that have to do with radio waves? And how often do people actually put cell phones close to their head compared to 10 years ago? For all we know it could be related to increasing obesity rates.
The radiation pattern isn't the strongest there, however. Antennae on mobiles will be strongest emitting from the back and sides, with less out the front. Any RF that gets absorbed by the body is wasted energy, so they optimise the antennae to emit away from the body in the typical orientation.