Mac can do that, but it's also up to the software. Software can either detect when the default audio device changes, or it can grab the device at startup and ne

Mac can do that, but it's also up to the software. Software can either detect when the default audio device changes, or it can grab the device at startup and never change. Google's software, for example, has demonstrated the latter behavior in the past for me (specifically, Google Hangouts has had a tendency to not notice if I plug in headphones+mic and continues to use the built-in mic instead).