Roleplaying games have always been defined, in part, by a very strong storytelling aspect that predates even computer games. Tabletop roleplaying games have always been based on a setting created by the game's designers, in which the players, usually through the guidance of a game leader or dungeon master, play out their own roles within the game's setting. This tradition has continued within the MMORPG genre, although it should be said that the strongest MMOs from the past decade have generally had the advantage of being based on an existing franchise. Of course the amount of players that actually play any RPG for the storytelling aspect varies from game to game, but this group has never been the majority.
That doesn't mean that the story is entirely unimportant. The storyline provides the motivation for the player to do what they do. What's unique about RPGs of the massive multiplayer online variety, is that most people pay no attention to the story at all. They play the game because it stimulates the part of our brains that enjoys watching numbers go up. Most RuneScape players don't slay Elvarg because she deserved to be punished for laying waste to the isle of Crandor, but because the quest gives a bunch of experience points and lets the player wear a fancy piece of armour.
When RuneScape was first opened up to the public, the philosophy of the game designers towards the storytelling aspect of MMORPGs was pretty obvious. There were no real factions and no real conflicts. There was a good god and an evil god, but all players had to go by to tell which was which was the fact that the good god has temples that look vaguely like churches and the evil god generally uses a lot of skulls in his places of worship. The quests, which have always been the main source of storyline information, basically consisted of either fetching some items or slaying some big bad monster. The only quest with a real 'story' to speak of was Demon Slayer, and even that wasn't much. Some big demon once almost destroyed a city, now it's coming back, could you please kill it with the same sword that was used to kill it last time around?
But somewhere along the line stories started to be incorperated into quests more and more. This started slowly at first, with quests such as Temple of Ikov offering brief glimpses into a larger storyline. This was only the first phase, as Jagex eventually began releasing quests with interconnecting stories. The first and most prominent example of this was the Plague City quest line, which was based on the outbreak of a misterious plague in West Ardougne. Over the years other quest lines followed, such as the gnomes, the dwarves, the Fremennik, and others. These days, the majority of quests released are part of a larger series of quests.
These quests have helped add some much-needed colour to the game, but they were only part of a larger process in which the game has slowly been given a larger history, with ages, god wars and mass migrations. This has occasionally led to some interesting retroactive changes to the game's continuity. However, as it stands today RuneScape has an established overarching lore. We have reached the point where in stead of quests being used to build up the storyline, the storyline forms the frame in which the new quests are set. The world of Gielinor now has enough of a history that novels can be written about it.
By creating a story to give each race and faction a place in the world, game developers can add some much-needed colour to the game's settings. A lot of a people's culture and behaviour can be explained by their history. For example, the gnomes' distrust of humans has always been one of their main characteristics. When they were first introduced in the game, all that was given as an explanation was the aggression of Khazard towards them. By expanding on the way individual gnomes deal with this aggression and Khazard's motivations behind his aggression, players are invited to become emotionally invested in more than just the experience and material rewards that come from resolving the quests surrounding these stories.
All this is part of the larger overall development of RuneScape as a game. The game has grown from being designed and run by a team small enough to fit into a three door car to a massive corporation employing hundreds of people making millions of euros/pounds/dollars/etc.. In the same way, the story of the game has grown from random fetch quests and killing random monsters to epic clashes between gods and men, evil plots to take over various parts of the world, and searches for vast ancient treasures.
I personally am a huge fan of the stories behind computer games. Great stories have helped me sit through mediocre or even bad games. By presenting the players with a story fitting the size of the game, the developers of RuneScape have taken a huge step forward in developing RuneScape from a cute little project to an MMORPG that fits modern standards. Even if it doesn't have the huge budget or the spectacular special effects of commercially developed MMOs, adding a proper story to the game has been a huge step in the right direction towards making RuneScape a better MMORPG.