Apple will reject any app containing a mic icon

No they won't. They will reject any app containing a mic icon that is not being used for dictation. The Chrome app uses a mic icon for dictation.

All these microphone icons are nearly identical in style. Try one that doesn't look like a large-diaphragm condenser mic in a radio studio.

http://en.wikipedia.org/wiki/File:Sound_Recorder_icon.png

Apple has always been clear with developers that any system wide icon they use cannot be used for any other action. For example if you use the 'i' (info) button for anything other than showing information (usually by flipping the view) you will get rejected. It helps maintain consistency.

All the app shown in the example have used the iOS Siri/dictation icon to do something other than launch Siri.

Also, why is everyone using that mic design? Very few real world mics actually look like that anymore. Why not use something people are more familiar with like a standard dynamic mic shape?

Seems Apple want to avoid any confusion with the Siri mic. I used the standard mic icon in quite a few apps so I'm going to need to take a look at the best alternative, unfortunately.

It's kind of a shame. In my opinion, the microphone icon makes for the best user experience because there is no ambiguity about what it is going to do when you press it.

With a talk bubble or a picture of a robotic head you can guess, but it is not immediately clear.

It's interesting because it seems like Apple wants to avoid confusion for users thinking the app is Siri by hurting the user experience in each of these apps.