Halogen Headlight replacement

I had the passenger side headlight burn out this week at 40k miles. I had replaced one headlight bulb at about 20k. So I thought it must be the other original bulb finally burning out. Well after pulling the bulb I found that it was the newer Phillips bulb that had burned out. My wife likes to use the headlights as DRLs so I figure I got 1300 hours on the replacement bulb. Since I bought the Phillips bulbs as a set of two I put the second bulb in.

So much for the often given suggestion to replace both bulbs at the same time.