I'm a bit of a history buff so I think about stuff like this. Revenge of the Sith takes place about twenty years before A New Hope (19 years before the Battle of Yavin according to Wookieepedia ). But Han, Luke and many others seem quite ignorant of events before Order 66 was implemented.
So that we're all on the same sheet of music let me explain that I will only be referring to the six movies (in their original non-special edition versions) and will not reference any Expanded Universe material.
In Episodes II and III we have a major military conflict being fought that is referenced exactly once in Episode IV. I can buy that. Using a real world example Desert Storm doesn't come up in everyday conversation for most people. And I wouldn't be too surprised if a lot of people couldn't place the name Norman Schwarzkopf.
But Obi Wan Kenobi isn't just some old general. As a Jedi Master he is on the Empire's Most Wanted List yet has been living pretty openly under a slight variation of his name. On the other hand Tatooine is one of the armpits of the galaxy so it's possible that Old Ben Kenobi stayed under the sensors.
The names Kenobi and Skywalker don't ring any bells when Han Solo meets Obi Wan and Luke. Even though Obi Wan is dressed like a Jedi Master and has just used a lightsaber.
In places like Coruscant and Alderaan the average person may be more familiar with pre-Imperial days (For example Leia's knowledge of Obi Wan Kenobi) and I wonder what is common historical knowledge on the core worlds.
"For over a thousand generations the Jedi Knights were the guardians of peace and justice in the Old Republic. Before the dark times. Before the Empire." - Obi Wan Kenobi
Apparently the Emperor has done a decent job of erasing the Jedi from common memory. In less than twenty years the Jedi Order has gone from a major player on the galactic stage to a myth for those too young to remember. How much of the Jedi Order's rich history has been lost and how much does Luke Skywalker know in Episode VII, set about thirty years after Return of the Jedi?
In this period about fifty years after the Empire was formed what is remembered about the pre-Imperial days? Going back to my real world example, if Norman Schwarzkopf isn't well known now, William Westmoreland and Curtis LeMay are even less known.
To be fair, some things will never be forgotten.
Yes, Episodes IV, V, and VI were made first so of course they don't much reference specific events in Episodes I,II, and III. This is just me overthinking about stuff as I am sometimes wont to do.