CSS Shapes are still pretty new; looks like support is only there in the newest version of Chrome: http://caniuse.com/#feat=css-shapes
Even chrome and firefox, which auto-update their browsers in order to keep everyone on the latest version - which should let websites use new features earlier - seem to have around 1/4 to 1/3 of their users on old versions,
http://cdn.arstechnica.net/wp-content/uploads/2014/09/chrome...
http://cdn.arstechnica.net/wp-content/uploads/2014/09/firefo...
which is worrying.