Well yes the headlights are on whenever the car is running( taillights also, for that matter). Therefore the bulb's service life will be shorter than if it was on only at nite. I'll bet the dealer replaced them both. Anyway, compare the cost of a bulb ($8) to being involved in an accident because the other person didn't see you coming. The bulbs are easy to replace (no tools, 2 minutes tops). I carry one in the trunk at all times. You can disable the daytime running lights if you want to. Instructions are in the owner's manual. First time some cretin pretending to be a licensed driver pulls out in front of you, you'll probably enable them.