Why does it matter? Oil tempered springs have been around for a very long time and they are the most common springs on a garage door.
These spring have one downfall, they rust. These springs are nice because they keep their tension and rarely ever need to be tightened. Anyone who suggests tightening torsion springs is wrong - you are temporarily helping your garage door. The fact is that the spring has a limit on how much it can be adjusted, if you over exhaust that limit then you reduce the cycle life. Cycle life refers to the rating of the spring to go up and down. One cycle is one time up and one time down. Most cases people should look for springs and parts with a higher cycle life, that is unless you love taking the garage door apart. Oil tempered springs rarely needs adjustment, but do not look as pretty as their counterpart, the zinc galvanized spring, which is not going to rust.
These springs look nice and most customers think they are nice because they are pretty. This is hardly the case when it comes to longevity. The other issue with the zinc spring is the noise it makes. It makes a weird sound when it rotates that becomes very aggravating at times.
As far as cycle life - both these springs have the ability to improve. There are plenty of cycle life conversion tools. I would recommend at least going with 20,000 cycles. The trick is as the cycle life of the garage door spring goes up, the wire size increases as well. That's why you can't go to a super high cycle life - because the spring price will go through the roof. The cost to ship the spring goes up as well because its more metal.
It's important to remember that the parts on the garage door have cycle lives as well, I would highly recommend that people buy new bearings and new cables if they are going to take the time to switch the springs out. These parts are usually rated at a lower cycle life than the new springs you are going to be putting on the door. Why take the time to take everything apart and not switch the parts as they go bad?
If and when the cycle life goes bad on the torsion tube, it will start to make the springs struggle to rotate. This will in turn, lower the cycle life of the spring tremendously. Companies will not warranty springs if the bearings or the rollers are going bad.
The rollers affect the spring because if there is a large amount of friction when the door is moving, then the springs will have to do more work, which is the last thing you want. This is what can reduce cycle life as well.
When you get the springs installed, make sure you spray them with an all purpose garage door spray. Be sure you spray the hinges, the rollers, the bearing plates, and finally the springs. I recommend once a quarter.