Lego is some kind of cultural icon now, and many people want to participate. That's why they have tons of sets aimed at adults over many themes, like plastic flowers, formula 1 helmets, old video game consoles.

Many of them are a really bad and expensive purchase if you only care about the theme itself, like the latest Death Star (or almost any Lego Star Wars set). You can usually buy a similar and cheaper non-lego model. Or the Titanic set too.