The ROTJ Tatooine trip actually made a little sense, considering the fact that we first meet Han there in ANH and are concurrently informed of the price on his head. It's not a huge stretch of logic to see Jabba as connected with Tatooine, particularly if you grant the SE Jabba scene as authentic. Add to that the fact that Fett delivers Han to Jabba, and you've got a nice little coincidence in the appearance of this "backwater" planet twice in the trilogy, but by no means an unbelievable or overly "convenient" one.

PT Tatooine superfluousness, on the other hand, just stretches credulity to the breaking point.