Andy,
People who do not accept the fact that TO-92 transistors dissipate the heat through the leads maybe know the thermodynamic model of those transistors. Some heat is dissipated through leads, but mainly through one lead only: the lead with the bond pad. The chip is mounted with silver filled epoxy on the pad of this lead. The others are just connected to the chip with a thin gold bonding wire with low heat transfer capacity. Furthermore, a good part of the heat is dissipated through the thermoset plastic encapsulation. This material is designed with specifications for thermal conductivity for the purpose of conducting thermal energy away from the chip. If you touch an overloaded transistor with your fingers, you will quickly change your mind.
73, Jakob
