Nearly everything in a Volvo is actually computer controlled
(so-called "fly by wire"). In the case of lights, it can detect a
blown bulb and then display a  warning message. About the only
actions not controlled are steering and "normal" braking. Even
those may change in future models with all the anti-skid,
anti-roll, anti-this&that they are building into new Volvos (and
other makes).

In an earlier contribution to this discussion,

Not sure about front fog lamps - but rear fog lamps need some logic to stop
them being used accidentally. A few years ago, this would have used a
latching relay and momentary switch - but it's probably cheaper now to let
the computer do it.

The idea is that you should only be able to switch on the rear fog lamps
when the ignition and headlamps are on. Having done so, if you switch the
ignition and/or headlamps off and back on, the fog lamps should *not* come
on again without the switch being operated again.

 [ ... ]

Why not, it's babysitting all the other lamps, not to mention a
lot of other stuff.

This is an ease-of-manufacture issue. From a manufacturing viewpoint,
it's much easier to run a fat power wire and a skinny network wire to
each point where there's a device (i.e., light bulb) to control. Or,
a cluster of devices... This allows having a single connector with two
or three contacts to connect a light assembly having multiple devices,
like a tail light, turn signal, backup light, and brake light.

The cost savings of not having to run all those individual wires in
a harness, not to mention the easier dealer maintenance with so much
less wiring to trace/troubleshoot, saves tons of labor--it takes
less time to run one two-wire cable to several points, just plugging
in one small connector at each of those points.

The largest component of manufacturing costs is labor; labor cost is
directly related to time; reduce the time required, even with the
tradeoff of higher material prices, and the savings can be huge.

Since the control modules can be dirt cheap in volume (although not
necessarily at the dealer parts counter), it's trivial to add in
sensors (bulb out, temperature, etc.) and adding a device to a circuit
is as simple as crimping another little connector to the cable.

Modern cars are networks.

Gary