Part of the problem is player attitude, but we all know John Gabriel's Greater Internet F@$!wad Theory. There isn't much that can be done about that issue, so the best solution is to find the core of the problem within the games themselves.
At the core, the issue is about soloing and how it has become the de facto design focus for most developers. One of the few development teams who seem to be focusing on new group experiences and powerful guild tools is EA Mythic. A point Ethic makes in his post is that developers should be focusing on giving people reasons to really want to group together. I fully agree with that sentiment, but don't get me wrong when it comes to solo play. The solo experience is important as well, but it is not the essence of a massively multiplayer game.
Unfortunately, developers can only put their resources into so many features before spreading too thin. A smart developer in the current industry would take a look at the solo design and conclude that it's fine for the time being. Sure, it could be further refined, but there's been enough of that in recent years. What I'd much rather see is a stronger focus on groups and guilds. Grouping and guilds are easily the most important factor to the social experience -- which is why...
Groups Are Good
Lets work from bottom to top and start with groups. The first thing that should be made apparent to a player is that grouping rewards more than playing lone ranger. Aside from shoving some giant text into our faces that says, "Hey you idiot, find a group and get more stuff!" the next option is to covertly convince us all that groups are good.
Some of my fondest memories have been playing with groups in Final Fantasy XI. Of course once you hit about level 10 or 12 groups were a necessity (at least back when I played) and finding a group could be a pain in the ass. That was a forced situation and it pissed me off that I didn't have the option to solo. However, once I started to group I found out about skill chains. These are awesome events where players tactically link different attacks together to form different bursts of damage or elemental effects. In short, it was plenty of good times working with each other to pull these off and kill mobs even faster.
Mechanics that focused on cooperation are what kept me hooked for FFXI for several months, even if I did wish I could solo during those long hours of waiting for the right group. Warhammer Online features a new type of quest called "public quests". I'm sure plenty of people are familiar with PQs, but just to be safe I'll do a quick overview of them.
Imagine you're a big Orc and you come strolling by this group of other Orcs trying to bash down some big shiny Dwarven fortress door. Well you can't help but investigate, so you walk over to see what's up only to have a bit of text pop up on the upper-right of your screen. It innocently lets you know that if you help collect 100 barrels of booze for a giant troll that's standing nearby you'll get a some good loot. This is a quest everyone else sees and can contribute to freely. The more you do the more you gain and that's the basics of a public quest. There is a bit more too them, but that's foundation of it. These are supposedly littered about WAR and are perfect for enticing players to cooperate leisurely -- which leads to more grouping at end-game.
The next step is to give players a tool to easily find other players no matter where they are in-game. This is where a game like City of Heroes comes in to save the day -- um, figuratively in this case. With a robust player finding feature that allows anyone to find people based on level, class, interest in activities such as questing or just grinding and location we're off to a good start. Grouping should consistently be encompassed and encouraged by the game, otherwise people will opt out for the solo experience. For the moment, WAR seems to be the only game willing to borrow the better bits from other games while adding their own innovations at a reasonable tilt.
But Guilds Are Great
A problem with guilds has always been player resources. Not every guild has the required resources to run a website, forums and other various services many players expect from them -- they're casual players. What would be great is if a developer offered a more robust tool set to all players. I already mentioned that EA Mythic is working on some of this with their concept of a "living guild" that has its own levels and rewards for reaching those higher levels. Their focus is to give players a reason to stick to one guild over the course of time, which is honestly something I think many other developers should learn from after WAR does it.
There have been a lot of predictions for 2008 and I by no means can say what will happen with Warhammer Online. I do think they've got a lot of pressure to deliver a million dollar subscriber game and that they'll do everything that they can to get those numbers. In a game where war is everywhere, grouping together seems like something you'll want your players doing more than anything else. Not out of just necessity, but because as a game developer you know it's more fun than the solo experience.
So regardless of whatever happens with WAR, I think we can all agree that bringing the fun to groups and guilds is what we should all be asking from developers. It shouldn't just be isolated experiences that some people have, but common experiences that we all have on a consistent basis.