vaderios said:

Did you notice that in PT to release someone of his chains its simply requires a touch of lightsaber. In ROTJ luke tries too long to release Han and Chewie. Can be done something there?

-Angel

You've seen the size of Luke's lightsaber, he would have burned their arms off getting it that close to them!

But seriously, maybe Luke wasn't as confident (or careless) with his lightsaber and was afraid of cutting them by mistake. I know I would be. Seems too casual in the PT, maybe it was supposed to be.