Leap seconds are announced months in advance and can only occur in 2 possible positions in an entire year. It's pretty standardized, especially compared to the mess that is daylight savings time, where changes can be announced only a few days in advanced (e.g., Egypt) and possibly even retroactively.

The problem with leap seconds is that time is often represented internally as seconds from the Unix epoch, and this simple integer counter assumes leap seconds don't exist. In effect, there is no way to actually represent a leap second in many computer systems, so the question of what you do is basically a choice of the least painful lie. Handling leap seconds in the situations where people care about them requires a lot of complexity for an event that happens only once every few years.

There's a movement to abolish leap seconds, which I am very much in favor of.