[phkahler]

>> The YouTube play/pause button shows the action it will do, not the state that it is in.

A lot of physical play/pause buttons show both symbols. Also in a lot of cases you can tell if a video is playing.

[dotancohen]

Not if it's buffering because you know that you have a bad internet connection. Around here, I often see people skip to an earlier portion of the video to check if it is playing or not.

And that is anyway besides the point of consistent UIs' toggle switches describing their state, not their action.