Thanks for this. I confirm this is no longer a problem with both the ClipToPlotArea option and the Q2 2013 SP1 release.
However, I am still getting some clipping of labels, this time in pie charts (see the attached picture). In that chart, I gave the labels a margin of "-4,0,0,0" so that they would not sit within the sections of the pie, but outside, just like this is done in your example (at http://demos.telerik.com/silverlight/#ChartView/Palettes
When the drawing area is roughly square, there is no clipping, this only happens when the drawing area is rectangular (the height is > width).