I've recently watched and read the anime and Tokyopop translated novels, and found it awesome. (Though the Tokyopops seem flawed; inconsistency in the rank of Lef, timing of FTL vs. the Nova Sicilia treaty, etc.) Unfortunately, I seem to have found the dark side of being a fanboy, thinking so much that I find flaws in the sociology.
* raise their children themselves, as family-supported single-parents, until high school; this helps maintain pure family traditions, undiluted by spouses.
* Despite a fair bit of personality variation, seem to have a highly uniform culture, with shared ideas of honor, not backing down, and revenge; and all are described to be atheists.
* Descend in large part from 29 individuals, but also frequently elevate humans to the rank of Abh, their new children to be incorporated into the race.
These three things don't seem to fit together well. Frequent immigration and no institution for early acculturation don't add up to uniformity. Samson's an Abh, right? So if he has blue-haired kids, they'd be being raised with his cat-eating habits. Jinto, who admittedly has a nearly unique background, could easily try raising his kids to be Presbyterian Fundamentalists (apathetic) like himself. Lander-Abh might well have desires to 'marry', even if it's not legally recognized, and that might get picked up.
There's some countervailing forces: Jinto being jumped from Lander to Count is probably nearly unique; most humans would be promoted for service in the Star Forces, and adherence to Abh military culture. High schools and general osmosis would have some effect, as would the biology (not getting drunk, long lifespan). Nobility have to serve in the Star Forces, giving more time for them to be beaten into shape. Still, seems like there should be a fair bit of diversity (culinary, religious, familial) among the Abh, especially among the masses of 'knights'. Fanfic about Jewish Abh?
I guess one other element is double-edged. Abh reproduction means that there's not even the pressure of sexual selection, of needing to be acceptable to a mate; you can spawn kids on your own. OTOH, such reproduction interacts oddly with traditional religions. And finding another Abh -- especially an unrelated one -- who's also into marriage and your religion might be hard, with minorities self-quencing due to being minorities. Though there's Abh-citizen or Abh-subject relationships to consider.
In the end, both norm enforcement and law enforcement seem underspecified. The Baron Febdash arc (or book, at least) made brief reference to noble legal council, and we know there are laws, but not much about how the government or economy work.
All right I've got something to kick of a bit of discussion.
The (genetic) Abh. Homo Sapiens Astro or Homo Astro? Or in laymen's terms are the Abh a sub-species of normal Humans/Terrans or a completely new species in the human family tree?
I'm inclined to say new species but what about everyone else?