Rationalization said:
Original series had no problem with ignoring continuity and then making stuff up later. *Cough* Vader killed your father. *Cough* Why can't the prequels do the same? Not to mention all the other stuff that just doesn't make sense, 1 man plots millions of people against each other destroys the jedi order and forgets that a few laser blasts from the outside makes their planet destroyer explode? Vader goes past the point of no return then returns from the point of no return? Why can't the ghost jedi's do anything if they were made more powerful than before? Reminders to use the force is tape recorder power. Why is there no DNA protection so that someone other than a clone will be noticed if they're walking around as storm troopers? Isn't the emperor the most powerful sith to ever live at that point? Why couldn't he find luke?
Well, actually, the part about Vader being Luke's father was a part of the plot all along and that was explained to an acceptable degree within the trilogy.
The bit about the emperor plotting millions of people against each other is discontinuity between the old and new trilogy and the Death Star being blown up was one weakness that could only be found through careful analysis of the battlestation's plans. Top it off, the emperor was probably not a mechanic, so there's no reason to expect him to know about it. It also doesn't help that Lucas portrayed the Jedi as legendarily thick in the prequels. I mean, Mace Windu has a line "I sense a plot to destroy the Jedi." What, he needed to use the force to see what anyone paying the slightest bit of attention could see? Bah!
The point of no return was a belief held by the Jedi. I always took Vader's redemption not as a point of discontinuity, but proving that there really is no point-of-no-return and the Jedi were simply wrong about it.
No DNA protection? That's a retrospective plot hole because at the time, we hadn't developed that kind of technology and it hadn't really been discussed in sci-fi literature, so it was one of those things Lucas probably just didn't think of. It is still a plot-hole, though, I will give you that.
The idea of the the emperor being able to find Luke easily is treating the force like all purpose plot resolution. There were lots of factors working against the emperor, none the least of which being the light side of the force itself (and Obi-Wan being a part of it) potentially clouding his ability to see everything. The emperor was clever and had a lot of knowledge and power in the Force, but he wasn't invincible or all-knowing. He just thought he was.