I think roadkill2 nailed on the head, it does make them stronger to a degree but i'm no expert i'd compare it to a driveshaft you don't see any solid driveshafts.
Speaking of axles is there anyone on here that i can order through and ship to Australia. I've tried a couple of shops here in oz and they're telling me 12-15 weeks shipping, must be on the slow boat around the world.