The subject of insulation is an interesting one.
We insulate our bottom section because we are retailing and want to show that we have taken practical steps to make our product 'user- safe'.
Tucker poles, Brodex Pro-long poles, Omnipole Power-poles etc., all are fully conducting (being aluminium) and no one ever seems to have a problem with them.
I personally use a Super-Lite™ with no insulated section as all of the commercial jobs I do have no over-head electricity cables (all legally have to be underground nowadays). I have however worked in a thunderstorm and watched the lighting getting closer and at a certain point had to stop work until the lightning had passed over.
An interesting point with even fibreglass poles is that if the brush head was wet and the pole was wet, would it conduct electricity down to the user? I think so, so in a thunderstorm it would be most unwise even to use a fibreglass pole as chances are you would still get fried! The same would apply with high voltage power lines as how often are your poles bone dry?