Currently, if a headset with mic is plugged on chromeos, tray audio UI lists both internal speaker and headphone, internal mic and micjack. This gives more freedom that user can playback-to/record-from either of them.

However, I guess when headphone is plugged, few user may want to playback through internal speaker (if they want, they can just unplug the headphone, right?). We probably can add UMA to record the stats of playing back to internal speaker with headphone plugged? Same for internal mic.

Consider when headset with mic is plugged, do not list internal nodes, and default playing/recording from plugged ones. That is what mac is doing. No try for linux/windows yet.

This also helps  issue 658048 .

This is a UI/UX decision.