MacOS – What applications enable AirPlay mirroring for Mac

Airplay isn't a protected transfer mechanism, in the same way that playing (for example) a Blu Ray disc over a HDMI connection that supports HDCP.

High-bandwidth Digital Content Protection (HDCP; commonly, though incorrectly, referred to as High-Definition Copy(right) Protection) is a form of digital copy protection developed by Intel Corporation to prevent copying of digital audio and video content as it travels across connections. These connections include popular ones like DisplayPort (DP), Digital Visual Interface (DVI), and High-Definition Multimedia Interface (HDMI)

The system is meant to stop HDCP-encrypted content from being played on devices that do not support HDCP or which have been modified to copy HDCP content. Before sending data, a transmitting device checks that the receiver is authorized to receive it. If so, the transmitter encrypts the data to prevent eavesdropping as it flows to the receiver.

That's pretty technical, but in short (and this is not particular a developer choice, but the content owners choice) if they cannot guarantee that the content is fully secure end to end, they will not allow it to be transmitted. Airplay isn;t fully secure to the same degree as the above, and so many contents owners will not agree to it's use.

There are restrictions on Airplay in Mountain Lion. It has to do with your video card that comes on the machines that you are using.

Your video card has to be powerful enough to do all the heavy lifting of streaming so that your CPU is unhindered and therefor you can smoothly still use your machine.

This question and answer should help you out and explain things and find an alternative, such as AirParrot.

Here is an Apple Support Article on the subject, listing the restrictions and giving more information on how Airplay Mirroring works.

Here is the excert from the article showing the compatible computers:

iMac (Mid 2011 or newer)
Mac mini (Mid 2011 or newer)
MacBook Air (Mid 2011 or newer)
MacBook Pro (Early 2011 or newer)

As for a Mac Pro, they are not listed as a compatible model that supports Airplay Mirroring, as discussed in this article here.

You can still connect a cable and mirror in that sense, that has not changed in ML. The mirroring feature of using a separate display is a completely different process than Airplay Mirroring.

I hope that this answer helps you out.