Why did they...

Here is an issue that I've always wondered about- or rather, that I've wondered about ever since I was old enough (and geeky enough) to really THINK about the Star Wars movies and not just experience them. What question? Why, this one:

If Kenobi and Bail Organa were trying to hide Luke Skywalker's existence from his father (Vader), why did they allow him to keep the surname "Skywalker". And for that matter, why did they take him back to Tatooine to live with his Aunt and Uncle- who were known to exist by Vader. I understand how remote Tatooine was, but wasn't this taking an unnecessary risk? I mean, unless the name "Skywalker" was like "Smith" or "Jones" in the Star Wars universe, couldn't that name have set off flags if were ever discovered? Even if nobody knew that Vader WAS Anakin Skywalker, couldn't the name itself have aroused suspicion. Wasn't the Emperor's 'Inquisition' searching for hiding Jedi or even Jedi bloodlines? Certainly the name Skywalker might have stood out. Even if the chances of Luke's name being discovered were REMOTE (perhaps he and the Lars weren't registered Imperial citizens?), NOT changing the name still seems like a mistake.

You know, come to think of it, maybe that was another reason why Owen Lars stopped Luke from sending off his application to the academy. Maybe he knew the name WAS a liability. I'd like to think that the Lars were (before their deaths) on the verge of "spilling the beans" to Luke about his name and heritage- including the dark parts of it. Afterall, if a "Luke Skywalker from Tatooine" suddenly applied for the Imperial military, some warning flags might have been tripped.

But then "Luke Lars" isn't a particularly heroic sounding name. So...

Anyway, it was just a question I've always wondered about.