Triathlon distances

What I don't get about most triathlons: the swims are usually short, often not even half-marathons. My casual swim workout is longer than most tri swims. These are followed by ridiculously long bike rides and marathon or longer runs.

IronMan Canada, I'm looking at you. Which of these things is not like the other?

• A 180 km bike ride
• A 42.2 km run
• A 3800 m swim