If you want to see the history of RuneScape, all you have to do is log into the game and look around. You'll know it when you see it; it's that distinction between those cities that have their own personality and those that are just a collection of buildings, the more fluid mechanics of a puzzle or minigame, or the point where the quest you're doing stops being a combination of puzzles and dialogue and starts telling part of a larger story. The longer you've been around, the more changes you'll notice.
Depending on how long you've been around, you'll notice that the community evolved alongside the game. As much as we love to ask why it changed and point the finger at an update we don't like as the primary cause, it's more of a response to the changes in the game itself. Players gather around the day's popular moneymaking methods and pastimes. When those were trade and skills, the community developed around them. When bosses took the spotlight, boss hunting communities followed. When Dungeoneering was released, like-minded players formed groups to get the most out of it, and so on. The community is directed by content.
As for why it changes, the obvious answer is 'updates'. In 2005 and 2006, we received higher-level content through slayer and the Barrows, and skill capes to reward those few players who managed to get a 99. 2007 marked the shift from resources to boss loot as the commodity of choice when the God Wars Dungeon brought an entire new tier of equipment to the game, and when the removal of free trade and the wilderness crippled both PvP communities and the multitude of businesses and merchants that had set up shop before them. Raw resources stopped being a commodity and a gathering point for skill-focused players and became an avenue for skill advancement after it became more rewarding to use them than to trade them. The transition to new skills such as Summoning and Dungeoneering, from minigames like Castle Wars to ones like Mobilising Armies, and from quests like Wanted! to quests like While Guthix Sleeps, reflect these changes and reward higher-level players with worthwhile content. And as a result, players form groups that help them take advantage of these updates more thoroughly.
In short, it’s co-evolution between Jagex and their players, and contrary to popular belief, it hasn't killed the community. It has, however, made player interaction less direct. We don't trade face-to-face, and though we share skilling spots, it's rarer for conversations to pop up than it was in the past because of updates like the clan chat system; like-minded players no longer have to be in the same spot at all times. As in biological evolution, success isn't a guarantee. Clan citadels and clan avatars can be seen as an attempt to combine both styles, with mixed results, and the return of free trade and the wilderness last year didn't have the results everyone thought it would for the same reason: both the game and the community had changed past the point where such updates would have been appreciated.
Is the community dead? No, it's changed. It's less openly outgoing than it was when many of us started playing, but that’s to be expected when we have so many tools that make the game impersonal outside of our circles of friends. If you don't like that, there's a simple enough solution: talk to people. Skilling can get pretty boring without it.