I have some questions, why this music app present in CP is not the same of Microsoft Videos? And is there a way to pin music with this app like in Microsoft Videos one? Which app will be avaiable in RP? Same question about videos app, and why they did that with these 2 apps and not with photos?

You would have to ask the APPs Design Team which, had not finished its work by the release of Win8 CP; notice, says, App Preview

Cheers,
Drew

Totally agree with Drew. You would have to ask the APPs Design Team.