It doesn't need it in terms of "you can't watch the videos without it".

OTOH, I find such applications nice because they remove the unwanted overhead you get when loading youtube-pages in the browser.

ZouTube's what I use right now, but I remember mytube had a very different UI concept and gave details (on request) I don't have in zoutube right now.

I would appreciate having both fight for the best implementation.