[Normally I'd just have pointed it out on G+, but...]
The Most Important Encounter Table (IMNSHO) first makes it's appearance in the original City State of the Invincible Overlord by the Judges Guild, as part of the encounter sequence. Now this was a set of tables that determines the encounter you had in the city and is still one of the best examples of it's kind (even if you can meet a god walking the streets of the city). You don't have CSIO then you can also find these tables at the start of Judges Guild ready reference Sheets, Volume 1 (there never was a volume 2).
Anyway the table in question is simply this one (the very first table of the encounter sequence):
|1d6||Type of Encounter|
|1||Attacked by Surprise|
|6||Special Encounter (below)|
In other words the most important part of the encounter is why it is an encounter. After all the city is full of people (and other things), so why are these people important to the characters? The CSIO encounter sequence then goes on to determine what is encountered (from a patrol of constables [naturally quite frequent given that OD&D adventurers tend to be suspicious looking types, to a chamber pot being carelessly emptied out the window).
Most encounter systems in D&D work the other way. They determine the what and generally assume the why is an innate hostility (or use a treaction roll to determine how friendly the encounter is). The emphasis is on what is encountered, which biases the nature of the encounter. On the other hand, with the CSIO, with a dice sequence of 5, 5, 1, 6 you have a Troll sexually propositioning one of the players, which is a much more intriguing proposition for an encounter (admittedly only a 0.02% chance of it though).
Of course this table is rather simple. Midkhemia Press created a much more involved encounter tables with their Cities supplement (later repreinted by Chaosium and used in their Thieves World setting. Although the nature of encounter is second to what is encountered, you still have motivation as the primary drive of the encounter. For example you don't just meet a Mercenary Warrior, you meet a lonely Mercenary Warrior who wants a friend, or a band of mercenary warriors recruiting for a mission. Context is king.
This should be applied to wilderness encounters as well. After all what you encounter in the wilderness is likely to be out there for a reason themselves and will have a reason for why this is an actual encounter as far as the players are concerned. For example a hostile encounter of a single deer may not be of much concern, but what if the hostility does not come from the deer itself but a later encounter with the Royal Forester as they are enjoying the fruits of their chance encounter with the King's Deer.
The boardgame Tales of the Arabian Nights modifies it's encounters by adding a adjective. You don't just meet a Prince, you meet a Vengeful Prince or a Foolish Prince or a Mad Prince. One of the nice tricks (which works for the boardgame but is less suited for a roleplaying game) is that the player then chooses how they wish to encounter the Lost Prince. Do they Grovel to, Aid, Rob, Avoid, Converse with, Attack, Court, Abduct or Honour the Lost Prince? Which action will lead to a story that is of the greatest benefit to the players. They (and the gamemaster) have a lot more information to go on by knowing that the Prince they have encountered is "Lost," and that shopuld affect what everyone does.
[Just an idle thought whilst I slowly go mad repairing my RPG collection database.]