According to a Blizzard Developer, Mac OS X users will be able to listen to iTunes music and podcasts through the UI interface in Patch 1.12 and the Test Servers. However, explains the reason PC iTunes has no support.
Tigerclaw: “The Mac team cooked up the feature and got it working on OS X iTunes. For Windows, there were some hack/security issues to be hammered out – as well as deciding which music players to support, since there are many more choices – and waiting for all those issues to get resolved would have taken more time. It made more sense to ship the Mac implementation in 1.12 and use it to both satisfy the user requests we had gotten, as well as generate discussion and feedback for future revisions.
The Windows client has its own unique features like dual display support and Logitech G-15 keyboard & LCD support; iTunes support is presently Mac only, but we may be able to bring a similar feature to Windows in a future release.”