Just learned today that Youtube has deprecated the ability to remove the related videos that appear at the end of an embedded video. From now on, using the rel=0 as a parameter will merely show videos from the same channel to which the video belongs.
They’ve also changed a few other parameters, take a look here.
Seems they want you to watch more videos and this function was cutting into the continued watch time. Sad, since this made for a much better viewing experience in my opinion.