Actaully mike, thats not true, conrod failure at high rpm happens at the end of the exhaust stroke generally, this isnt effected by boost.

The difference in weight of thinner N/A pistons does lighten the load slightly though.

The two things that generally kill rods in a well built engine (ie not the big ends knackered and sending shock loads up them etc) are either too much torque killing the rods under compression or too much rpm killing them by stretching.

As such N/A rods never tend to fail other than at high rpm, and turbo motors are not any more likely to kill rods due to rpm than N/a ones, if that makes sense?
(accepting that a heavier piston will put more strain on the rods of course so if its a lightweight N/A piston that is fitted then you can get away with slightly more rpm)