Davey, I think that's actually got a reason behind it. The elevated, ornamental center of most roundabouts at least partially removes the view of a road going forward, hence it's like a "T" in the road where you need to concentrate on what's coming at you from your left.
Did see an elderly gent take a LEFT at the roundabout north of Lincoln on 66th and Highway 10 last winter. He stopped, looked both ways, took some time to think about, let a car come from the left through the roundabout, and then floored it to take his left-hand turn.