References to the comprehensive rules are best for everyone, new players included.
Imagine that the scenario where a new player is told by his gaming group that "at the end of the phase they take mana burn." The new player comes here and asks, "Do you take mana burn at the end of a phase? Lets assume for the moment that the highest voted answer is the correct answer that explains that,
No. You no longer take mana burn at the end of a phase. This is change in the rules.
The new player goes back to their group and says, "I ask about mana burn on the internet, and the highest voted answer says that it doesn't exist anymore." Their group might just reply, "So What! Lots of people on the internet say lots of things." This might be exacerbated further if the group contains a rules lawyer, or DCI Judge. What if that DCI Judge or rules lawyer has it wrong? (example: Prateor's Grasp - Can Opponent Determine Taken Card Before Shuffle). In general, a good answer will contain all the necessary information for the question within the non-quoted portion. The quoted comprehensive rules need only be read to confirm that what is stated by the answerer is correct. If someone is only interested in the correct answer, they can ignore the gray quoted blocks.
The Comprehensive Rules are the ultimate authority.
Even if a the rules will be going over their head, they can print out the rules quoted in the answer, and show it to whomever doubts them.
If we don't quote the Comprehensive Rules, the next official source of rules would be the M:tG Basic Rulebook. I am not sure that answers quoting that source would be much better. Examples below (titles linked to OP for comparison). If you ask me, it isn't much better, but we will see how many votes they get in comparison. With out any ultimate authority, who is to know if quoting the Basic Rules or the Comprehensive Rules is better, people on the internet will have to decide.