I'm at a total loss for words. I'm not sure I cannot even describe my thoughts on this change.
In the opening crawl, it says "The evil lord Darth Vader, obsessed with finding young Skywalker, has dispatched thousands of remote probes into the far reaches of space..."
Maybe this is just my interpretation, that says to me that he knows the name Skywalker already.
Now, Lucas has screwed that up, by now having the Emperor reveal who it is.