EDH/Commander is well known for it’s lengthy multiplayer games, lasting hours due to large deck size, eternal turns, and large amount of starting life total. However, poison and Infect, a mechanic primarily in the reduced the life total necessary from 40 (or 20) down to 10, cutting the amount of damage needed to be done dramatically. The mechanic Proliferate in Scars of Mirrodin block was also a large contributor, yet the source is the poison.
The rules committee has not changed that; in EDH/Commander, it is still 10 poison counters to lose the game.
The big question is: why hasn’t this changed? After asking the community, it seems that it’s split. With cards like Blightsteel Colossus, which can be placed in any deck and is a one-shot kill, it’s difficult to grasp why the total for poison counters hasn’t been raised to half the life total.
The answer may be in the game itself, however. The ways to lose in a game of EDH are as such: being at 0 life, being unable to draw a card from your deck, having 10 poison counters, and having 21 commander damage from a single commander in the game. The varying ways to achieve victory are part of the diversity of the game, and the only reason Infect is played. If Infect was raised to 20 (half the starting life total, which may be the intent of the mechanic’s design), it would be only 1 damage away from being commander damage. That would turn some players away from using Infect, and taking away from the diversity of the format.
Another aspect to consider is the multiplayer foundation of EDH/Commander. When a player starts using infect in a four-player game, the other three can clearly see the threat potential, and typically treat it much as we treat an infection: by cleaning it out. There may be one or even two players who get knocked out via Infect in the game, through a single-shot creature, Triumph of the Hordes or another means, but that’s perfectly alright-the game goes quicker and the other players now know better than to trust the deck when that mana is open.
It's clear that the Rules Committee might never up the amount of poison counters needed to lose in EDH/Commander. It diversifies the game, allows other cards to be played and strategies to be used, and gives players the chance to learn and experience a new strategy in a very large format. Long live the 10; may it compleat you and your game.