I'm an American living in Austria, with a discintly English-sounding name, with no German equivalent. People NEVER forget my name.
That's ONE name, not a whole cast's worth.
One or two "unique" names amongst all of the "common" ones is memorable.
Having a couple dozen names which are all unfamiliar to the point of sounding like gibberish becomes difficult and confusing quickly. This is for the same reason that is easy to learn
an unfamiliar word, but it is far easier to memorize a paragraph in a language that you are fluant in than one from a completely different language family.
The hardest time I ever had in keeping everyone straight while reading a history was a book called "The Washing of the Spears", which was a history of the Zulu empire focusing on the Zulu War that they fought with the British in 1879. A couple of the Zulu names stuck out and were easy to keep track of (Shaka and Cetswayo are the couple that I can still give you, years later). However, overall I had a hell of a time keeping all of the Zulus straight. The Europeans, with names that fit into the already well formed naming categories in my head, were *much* easier to mentally keep track of.
A lot of the confusion that does come up with "common" names has to do with the tendancy of them to overlap. You meet a number of Johns or Marys in any given week and all of the contexts start to get mixed up in your head. You notice that BSG does not bring this into play. There are no
other Karas or Lees or Sharons (aside from the other 8's; "Sharon" always translates into the same face) or Sauls; just the one of each name.
Star Wars was easier because they had a smaller cast of characters whose names mattered and the smaller cast size allowed them to stick to single syllables for a lot of them. They *still* used a scattering of existing names, and others that were direct plays on English words (the bounty hunter who would sell out anybody for the right is named Greed-o, for example; the last name of the loner smuggler is "Solo"; it has been pointed out that it not exactly a *huge* stretch from "Darth Vader" to "Dark Father").
As for Aeryn Sun: That's a
really poor example for your side of this debate. In the first place, when you
hear her first name in the show, it *is* an already familiar real world name. It just turns out that for the alien character they made up an alternate spelling. Her last name is a simple everyday word in English, not even an alternate spelling. Both said together become a sound-alike for an English phrase that is not entirely without meaning: "Air and Sun" (since "swallowing" the D in "and" is very common among native Aglophones, depending on what sound starts the following word).