I have the SA 8sp on 2 of my bikes. In one, an internal gear broke, somewhere close to 10,000km. If it wasn't for me making a repair, it would have been a write-off/replacement. Since then I have had trouble keeping it lubricated especially in wet weather. Mere mortals can't get hold of the original lube.
Both internal gears and derailer gears have their place.
Would you say the SA 8 speed is more fragile than the 3 speed?