Sean, here is my thinking on the matter of hard surface hazards or features that bounce into oblivion, and in this instance - a betting 19th hole.
Let's say we need to have a playoff, we played eqaully well or matched eachother's lack of skill for 18 holes of the match, however you want to look at it. We go to a par 3 playoff hole that is as TD describes, 200 yards with rock outcroppings within the various parts of the green surrounds. WE are both a bit anxious to win and would love to win based on superior play, (a fluk always deminishes one's enjoyment of a victory -wouldn't you agree). We are both a bit nervous and both either push or pull the shot. Both are equally off line and not well struck. One "carooms into oblivion" the other lands where a shot to recover for an up and down, or even a chip to a place where two putt is likely. Does that make for a satisfying ending? I just think that a green should be surrounded with terrain or features that offer some chance, albeit slim, and one that requiries great skill and guts at potential recovery, in order to make a more interesting hole.
Obviously, if one of the contestants actually hits a superior shot next to the flag, or in, and the other is off line, there is little doubt that the best shot wins. But, the luckier of two not so good shots (one to oblivion) isn't a desirable end to me. I think that hard structures near greens tend to exasperate this potential to unfairly penalise one offline shot over the other.