That's only some cars.

Many today still use open diffs. Some use open diffs and braking to produce a result that looks like traction control or a torque biasing diff.

Some cars use electronically-controlled diffs that can vary pressure on clutches using simple electric servos to bias torque - Bendix is a big supplier of such things to companies like Honda.

Others use hydraulics, similar to torque converters, to bias torque (e.g. Audi's original Quattro system).

And others use gearing to bias torque, such as Quaife differentials.

Factory systems (with rare exceptions) don't use locking diffs (GM has one as an option, others may).