A couple of weeks ago, both low-beam H7 headlight bulbs burned out the same day. These bulbs lasted about 650 hours (26,800 miles) of use. After putting in both spare H7 bulbs I carried in the trunk, I checked with the local dealer about this.

Seems there is a warranty upgrade to prevent this from happening. A replacement wiring harness has a voltage regulator chip in it that limits voltage to the headlights to 12 VDC. This prevents voltage surges during start-up from stressing the filaments and shortening the bulb life. Two replacement H7 bulbs are included. Installation time is about 10 minutes. And it's free, too.

S80 owners who've had short-life headlight bulbs might check with your local dealer for a fix to this problem.

Some model year 70 series have the same issue and a recall was issued
for those, too. Sounds like the same repair.

I had both low beams fail on my 98 S70 about the same time (4 years
for one bulb and 3 years on the other) and the local stores were out (went
to several and even met a couple other Volvo owners at the light bulb
rack -- truely did). On the 70 series, the high beam and low beam use
the same bulb so I swapped them until new ones could be found. Not sure
if 80 series use the same bulb but the swap sure saved me one night.

I havent yet seen where Volvo has any cure for S80s as they're not problematic like the X70s were before the recall. S80s have no headlight recall but like all newer Volvos, the headlamp bulbs are to be replaced as a pair.
If it were my car and in the US (not Canada), I'd get the daylight running lamps switched off which is easily done with the dealers Vadis cart for a small fee (not warranty).

I have a MY2001 S80, and replaced one headlamp and two rear lamps in the first 3000 miles. I was told by the Dealer that the factory "fix" did not apply to my serial number. However, he also advised that, if I complained in writing about bulb life, they were authorized to turn off the DRL feature under Warrantee. I wrote a sentence on my service order, and the DRLs were de-activated at no charge. The "off" position on my light switch now actually does something, and the lamps don't flash on and off during cranking.