I`ve got the same problem, and must say it is very frustrating.
I have decided to build an Android app (and pay extra), becouse even in Mag+ release 3.1, it was said that it "Can play embedded YouTube clips". http://support.magplus.com/entries/21297116-release-3-1
I have experimented a lot, and still don`t know how to do it nicely.
When I simply link to yt in embedded browser, it shows the video, but the fullscreen option is not available. I can play the video, but even when I close the window, I can still hear video playing in the background.
Mag+ Support, please help. I suspect it is a webview problem, but I am not sure. All I want to do is to embed my youtube video, just like it is embeded on any website and finish the project.