I'm not a Triathlete by any stretch of the imagination - but I do train a few. The strength requirements of a Triathlete are not necessarily different than any other athlete but you need to make sure that the strength training that they are doing is going to not only make them stronger but make them more resilient and less injury prone. There is nothing about a triathalon that doesn't put the body through the wringer - and with that in mind, the strength training that they do has to lean heavily on reinforcing the opposing muscle groups and increasing their mobility.
One technique that anyone that runs, or spends a lot of time on their feet, needs to do is the One Leg Deadlift. Just like the conventional Deadlift, the One Leg Deadlift trains stability, strength and "connection" with the whole body. The added bonus is that the One Leg Deadlift requires you to make massive connections and associations internally to stabilize not only yourself but the load as it goes up and down. While most people can't go very heavy on the One Leg Deadlift it can still be a powerful addition to any training program. Don't discount this one...
Another technique that haas to be an integral part of the program is the Turkish Get Up (or just plain old Get Up). I've written about this technique a number of time so search through the archives for all you can ever need to know about the Turkish Get Up. The most important take away point is this: if you are any athlete of any caliber you need to be doing the Turkish Get Up.
While the One Leg Deadlift and the Turkish Get Up aren't miracle workers they will fill in the gaps in your training program to prepare for a Triathalon or any other sport that you compete in. Get the training, do the work, reap the benefits!