Well it's poor design in that case, because you often end up with a big queue in the left hand lane and nothing in the right. And with regard to your last sentence local traffic will only start to treat it in such a way after a few people have made an example of it.
No, I am saying there are two lanes on the approach to the roundabout, and two exits from the roundabout (A283 south and A283 north - not a lot of traffic is going to go back where it came from on the A27 east). As such it makes sense that the left lane is used for the A283 south and the right...
This local example gets on my tits.
There are two lanes and two exits, therefore in this situation, it is acceptable to use the right hand lane to go straight on. Think it's only me that does it though...