It is not necessarily a "structural" slab. The last 4 homes I lived in had an attached garage (3 were 2-car and the other was a single car). The slab was free floating (no doweling) inside the stem walls, was unreinforced, but a couple did have wire for crack control. The slabs were 4" or 5" thick that were placed on a partially compacted base. This is very common construction where there is a desire for a stem wall to project about 4" to 8" above the floor level.
As a structural engineer, I can say these were not designed as structural elements and there were no structural requirements, but built by a home builder and concrete contractor with no specific reinforcing or connection requirements. - It just works.
No cars stuck in over many years and two of the four did not even have any cracks because they were not attached to the stem walls. It also makes for a garage that is easy to keep clean from debris and slope the slab as desired.