The text and stats indicate that these are identical but the numbers show some differences in effectiveness. Spider turrets are better at Fighters/Bombers than Sniper turrets. Is this just a typo or is there a difference in power that isn't making it into the hover text.
I assume that by "numbers" you mean the "strong vs." statistics, right? If so, it would be due to the differences in the results of the simulations run to determine those stats, due to the engine damage component (fighters/bombers with damaged engines took longer to get into range to plaster the turrets.)