I've always felt that scale was too "sci-fi" ish for the fantasy-esque Star Wars universe. Star Wars planets don't really feel like planets, more like islands in an ocean. They're "planetville" planets.
The "small moon" being the size of an actual small moon feels... weird.
Everything about Star Wars is modelled after pulp era stories transplanted into a space setting. A man-made ship that could comfortably house billions of people is firmly into the realm of "true" SF and doesn't fit into a pseudo-1930's setting. Putting such a huge number onto the Death Star (and the SSDs, which are each the size of Manhattan) feels like a midichlorians moment.
