Exactly. There is no need to see once you are in the roundabout as traffic yields to you. and I doubt you can take a roundabout with much speed unless you have a very expensive car or the center section is too small and is not requiring enough if a direction change so the cars treat it as a straight road.

The reason for the plants blocking view of merging traffic is that if you make things FEEL more difficult to cross people tend to slow down.
http://www.youtube.com/watch?v=f-tj-sD7Zpc