It all depends on load and operating conditions.
If a gear can be reasonably sized for the load and decently lubricated there is little benefit in hardening. Stock gears from distributors such as HPC, Boston gear at all are not hardened.
Hardening adds considerable extra manufacturing work resulting in a significantly more expensive gear. Not only does it have to be hardened, an extra step which may also need a more expensive steel to start with it has to be finished by grinding. If you are going to grind a gear might as well do the job properly to higher levels of precision. Having done that for a pair of gears you might as well make the housing really accurately so the shafts are precisely positioned. Having done all that you have something capable of taking much, much higher loads. Its the sort of thing you do for automotive gearboxes et al. If done on a one off or few off basis theres is also a risk of hardening failure under load with the hard case spalling off.
Your Startite bandsaw has modest power and there is plenty of room to fit an unhardened gear large enough to easily cope with the load. So Startrite kept things simple. Indeed hardened gears appropriately sized for the load might well have been too small and hard to design in. Far as I can see, if properly lubricated, those gears should last pretty much for any reasonable machine life. But seals do leak and who changes the oil on their bandsaw!.
Clive