SEOUL—A proposed design for a pair of high-rises here that observers say looks like the exploding Twin Towers of New York's World Trade Center was just one of many ideas—and far from set—a local developer said, after the Dutch architecture firm behind the idea issued an apology.

Big, multibuilding projects are a staple of the construction scene in South Korea, where the national government is even building a $20 billion city-from-scratch that will eventually be home to half of its ministries and agencies.

So...