Here's how this looks like as a pie chart (Nielsen & Comscore data), by the way: http://www.asymco.com/2012/07/13/how-many-lumia/

How that? Android would be 183°, iOS would be 122°, RIM would be 32°. You could easily see that Android is slightly above 50% – but I’m not really sure how the iOS marketshare would look markedly different.

Since 50% isn’t really a very important threshold (though that could be argued) I would very much argue against using a pie chart. (I prefer areas or lengths to angles.) Plus, a pie chart wouldn’t make it easy to add platform subdivisions.