Actually, researchers in this study used green tea extract, but let's remember that the extract is a subset of all the wonderful natural compounds contained in brewed green tea. Scientists are only now beginning to identify and understand those compounds. Who knows what they are overlooking now? Pop a green-tea pill and you may be missing some as-yet-undiscovered compound. Drink an infusion of natural green tea, and you're getting all of nature's bounty.
Besides, a cup of hot green tea tastes much better than a pill. It's more relaxing, too.