Mechanical drives fail. I wouldn't spend $70 for a DVD drive, when you can get a Samsung or Asus for $20. You could replace 3 of them for the same price as one Superdrive. How often do you really need an optical drive anyway?
Myself, I use Samsung Blu-Ray drives with my Macs so that I can rip Blu-Ray's and they run about the same cost as a Superdrive that can't do Blu-Ray.