. . . what is preventing the axle from pulling out and leaving the bearing behind?
. . . try pulling a bearing off of the axle, and the reason becomes obvious . . . Sorry, couldn't resist. It takes about a 5 ton press to get the bearings on the axle to start with, so they're not going to let the axle slip out.

Actually, the Ford method is superior to the c-clip GM method in my opinion. If a GM axle breaks, the whole thing can come out, and you end up with a 3-wheeler. If a Ford axle breaks, it still ruins your day . . . but without the crash, fire, death and destruction.