In PSY's defense, although his apology was brief it also seemed genuine. It was basically a claim that he was young, stupid, and angry. The only Americans he knew were the soldiers that the media demonized, and he believed the media. Since then he has had a chance to travel outside of South Korea and meet real Americans, and his opinion of them has changed. He wishes he had never said those things now.
You don't need a long winded discourse, he offered a straight up apology for his past without anybody asking. You don't really think the White House demanded he issue an apology do you?