[veemjeem]

Plants grown in hydroponic systems tend to have shorter roots because plants don't need to grow deep to acquire the same amount of water. If you ever looked at roots in soil, you may notice many roots branch off into very fine whiskers, almost like the capillaries in our vascular system. Plants grown in hydroponics lack this whisker-like growth because it doesn't need it. Depending on the hydroponic configuration, long roots may not matter at all. For example, in a deep water culture grow, a very long root would just curl up inside the bucket, so it doesn't matter as long as the bucket has enough volume for all the roots.

[jmheflin]

You totally nailed it. I would just add that I am growing these vines for only 6 months before harvesting the fruit and discarding the cutting. They do not have time to put out really long roots. In addition, air pruning of the roots happens naturally when they run out of grow media, so they never get too long.