Yeah, I think I got the terms wrong - I've seen these referred to as "universal jurisdiction", but now I look the proper term for such laws seems to be "extraterritorial jurisdiction" rather than universal, for the reason you noted.

(FWIW, I think Australia's extraterritorial child-sex laws extend to long-term residents, not just actual citizens, and some nations extend extraterritorial jurisdiction to certain crimes committed against their citizens - for instance, Pinochet was arrested at the request of a Spanish court, for crimes committed against Spanish citizens in Chile.)

There's some discussion here (p. 26 in particular) implying that the USA's PROTECT Act might have true universal jurisdiction, but AFAIK this hasn't been put into practice.