The simple fact is that short of electrical or physical abuse, few of us really have a clue as to why our drives fail. Based on the useful life specifications, these drives will last long beyond any point where we still want to use them. My BenQ 1620s died in 3 weeks. My Liteon 812 still works; never burned worth a damn, but it still does after thousands of hours of ripping, scanning, and CD burning.
Given the $50 replacement cost, I long ago gave up trying to modify my useage to prolong the life of a drive. Other than my NEC 3500, I can easily replace any of the drives I use. My advice; use them for anything you want. None of what we normally do is abuse. Oh yah, and keep them cool.