Hi. Why there is no single Youtube app wich can show the videos in 1080p resolution? It' notorious! If WP Supports phones with screens capable of showing 1080p, there should be a dedicated app (a bunch of dedicated apps) to play videos in Full HD.
The Problem is that Youtube does not have a API for this. So apps that can play 1080p break on a regular basis because YouTube changes how the web player access them. This is why almost no app supports that.