Without discussing if Bluetooth and WiFi are bad for your health, it would be way better to keep those transmitters and receivers close to your head than for instance your upper body.
Your skull is quite dense and blocks radiation way more than the soft material that protects your heart and lungs.
Rather irrelevant in the GHz range, where density is much less significant than the chemical bonds and conductivity of the material. In fact the soft tissue would likely be a better absorber due to a higher concentration of water.
The technologies aren't the only important part; one should consider that a cellphone is talking to an antenna a few miles away, compared to the Glass talking to a device a feet or so away.
