This post is an aesthetic opinion post, but I feel I've been overly drone-y lately, so I plan on keeping it short. Or, at least, not as long as what I've written so far. I've come to the conclusion that the quintessential game mechanic that exemplifies what RPGs are all about isn't the "to hit" roll or skill roll or damage roll, it's the wandering monster table.
Board games, card games, and war games are about winning, or at least about showing off how good you are at the game. The rules of these games are designed to create an obstacle for players to overcome. Roleplaying games, with their combat encounters, their treasures and traps, and their puzzles, seem superficially to be like other games, but they aren't. RPGs are distinctive because of the fictional world the players participate in. RPGs are about Making Fictional Stuff Happen, as I commented on another blog.
When the DM in an old fashioned dungeon crawl rolls for a wandering monster, something happens that no one at the table was expecting. Sure, everyone knew it was possible, and the DM knew which monsters were possible, but that particular monster, at that particular moment, in that particular place in the dungeon? It's a new event. The "to hit" roll and damage rolls are important not because they allow one person to win or lose, but again because they cause Fictional Stuff to Happen that no one was expecting. So, too, do the reaction rolls, and the morale rolls, and obscure stuff like "% in lair". They make an RPG more than just a tactical exercise, more than a war game.
This is the spirit behind the various random tables in Dragon and other game magazines, or in the DM materials. They are not often the best-constructed or easiest to use mechanics, but in spirit, they are what RPGs are really about.