Love is where you find it. However I would say long distance relationships are Inherently designed to be temporary. Ideally the plan is to have one person eventually move to the other person’s location at some point in time. Most long distance relationships come about due to circumstances. (work assignment, college, military, or the couple met one another while one was on vacation).
Although technology has improved to the point where one can see each other daily using Skype or a webcam, sending emails, texts, as well as tradtional phone calls and mail; there is no substitute for being with one another. This is especially true if you are having a major disagreement. It's much easier to ignore or cut off ties in a long distance relationship when people are angry or upset. Even if you manage to make amends there is no traditional way of making up by being intimate or simply going for a walk together.
Last but not least, (loneliness can sometimes give way to temptation) especially if a couple is not able to see each other for long stretches at time.
One example is when high school grads go away to seperate colleges. Part of being on a large university campus are the social activities, parties, making new friends, study sesssions, and living life with zest. It gets old watching other couples spend time together, kissing, holding hands, going to dances, or even sharing pizza on weekends. It's human nature to want to celebrate your victories with the one you love as well as lean on them during difficult times. A congratulations phone call or hearing them say, I'm sorry it didn't work out over the phone does not offer the same comfort as being there.
Many high school sweethearts end up spliting up before the end of the second semester. In addition to all of the temptation and the overall environment on campus most students lack the finances to fly back and forth across the country to see each other on a monthly or even quartely basis. If one of them gets an apartment off campus they are likely not to visit where they grew up as much.
I suspect it may be a little easier to conduct a long distance relationship for mature adults who have the means to also travel back and forth to visit each other. Even with that there comes a point where if it is going to be a lasting relationship someone has to move. One man's opinion! :-)