Luke's training was assumed to have happened, and you saw the results of it in RotJ. The fact that Anakin's padawan vanished from memory and was never mentioned clearly highlights it as a retcon.
While right, i'll admit I was surprised at first at Anakin having a padawan. Though...to note, the movies just showed the start of the Clone Wars and then the end, so I don't really see the problem that Anakin could have had a padawan during the course of the war and something happen. But in the grand scheme of things of what was going on, there wasn't really any point to bring up Anakin having an apprentice, sure there was no mention of him having one....but at the same time there wasn't any mention that he didn't have one.
Thus leaving it open, to explain in TCW show that he did. The movies are just one part of the SWU, it tells and goes through the points that need to be made the other things can be sorted out in other aspects. You can't just rely on movies, to tell and detail everything otherwise you'd have such long movies. I mean in ESB, you only saw a portion of Luke's training and then he suddenly went to go fight Vader....when infact he actually trained for much longer then just a few days.
Which leads me to my point that the prequels should someday be remade in light of all the retcons and developments that happened after the films.