Also, I reject Kamikaze's premise.
From the parent thread, no one is claiming that solo games, in and of themselves, are bad. No one is saying 4e is "too good" for that, and that lone wolves are "badwrongfun". Yes, 4e does not actively facilitate lone-wolf style. That is not a value judgement.
The issue, however, comes down to this: conflicting playstyles at odds, and differing expectations about what the campaign should be.
A "lone wolf" playstyle and a "team effort" playstyle do not work very well in the same room together. And a group of lone wolves do not work well, without a lot of work, or a different system (see: Shadowrun).
It puts a strain on the DM to accommodate both playstyles, and puts a strain on the social dynamics of the players at the table. Not to mention on the game itself. If the Lone Wolf just walks off, and winds up in an encounter, he could drag the monsters back to the first group, or set off an alarm. The DM is also working hard to rope the lone wolf back into the group, to give him incentives to continue with what the rest of the group is doing.
It would be like being at a table where a Hackmaster group wants to play hack'n'slash monte haul, and one player wants serious intrigue and extensive roleplaying. He's in the wrong game, not because intrigue and extensive RP are bad, but because 1) his group doesn't want that, and 2) the game he's playing is counter-intuitive to that.
If you have a group that wants a campaign of player-vs-player conflict, and one guy who wants everyone to get along so they can save the world, someone's going to wind up unhappy.
Now, over in the parent thread, this is compounded by hostility towards Lone Wolves in general. Lone wolf players in a group-play campaign can be a major disruption to the game because they are trying to play their way, and everyone else is playing the other. This is my experience, so I have a bias against lone wolves in campaigns/groups/games not suited for their playstyle. Many DMs have a bias against evil characters, because people use "playing evil" as an excuse to be a disruption. Same situation.
A lone wolf playstyle, a lone wolf character, a group of lone wolves can work just fine if everyone is on the same page from day one. Case in point, "The Usual Suspects". All the characters work together because they have to. If one said, "Forget you guys, I'm going home", then either he leaves the story, or 1/5th of the movie is about that guy at his house, doing things unrelated to the rest of the story. The latter is what happens in an RPG, because you have 4-5 people writing the story as it happens.