Plus 1. With reasonable care, decent quality light cords will last a long time. If 12-36 month replacement makes you feel better, knock yourself out, but there are better ways to spend your money.
That's about how long mine last (3yrs). Most of the ones I've replaced were done because I needed something else anyway (ballast, I have gone through a couple of those). And I had a lighthead flood once. And before DR put strain relief on their cables I had a couple of those replaced.
Cuts in the cord have not been a problem.