Well, I think that my post in the referenced thread quite clearly puts me in agreement with Arravis, (and Mallus, nice post).
I play D&D with adults now. So there are two factors that come into play that aren't true with a juvenile group.
1. Most of the players have families and jobs.
2. Most of the players place a premium on their time. They enjoy D&D and want to play, so when they have a chance to schedule in a game, they very much want to make it.
Because of this, I can be entirely certain that if a player misses a game, it's because something serious came up that prevented them, and that they very much regret not being able to play.
At this point, I could dock the character xp, or I could just award full xp. I don't buy into the whole "you're rewarding people who show up" because as far as I'm concerned, if I as a DM am doing my job, the game itself is the reward for showing up. Being entertained for an evening by RPing a surly dwarf, talking to a lascivious baker who lives next door, fighting the mummies in the ancient sarcophagi...these are the rewards for playing D&D. The xp is, as someone else mentioned, nothing more than a signifier of power level.
Now, there are going to be discrepancies in power level. Mainly due to ability scores (my group likes to roll, though I've always prefered point buy), level loss due to deaths, and raw tactical ability. But no player of mine need ever feel like he's been handicapped at the game table due to events that were beyond his control.
In the end, D&D is a game. It's like parcheesi or, if you prefer, chess. Why should one player have to play without a bishop, just because his daughter had strep throat last week?