It's much easier for an N/A builder to make the transition to building turbo motors than it is for a turbo builder to make the transition to building N/A motors. N/A builders have to learn all the little things that turbo builders can typically get away without doing.
As far as stress goes, that's related to HP and RPM. Turbo motors can typically make power w/o revs, so they have a slight advantage there, but turbo motors also have a lot more parts that can potentially fail. In the end, reliability always comes down to the quality of the parts and how well the motor was put together.