For most of the history of MMORPGs there has been a tradeoff between great graphics and playability. MMORPGs are games meant to survive for years, and in order to gain and keep an audience the games are typically made to suit a broad range of hardware. The better the graphics, the more up to date the computer necessary to play without being inhibited by lag.
So when the new graphics standard of DirectX version 10 was announced, game companies were faced with the decision to support new graphics capabilities or to continue with the DirectX version 9 standard that was commonplace in the industry. The choice for many of the newer games was to offer the best of both worlds for players, leaving the choice of whether to go with DX9 or DX10 up to them.
There are some major differences between how DX9 and DX10 utilizes the graphics card to present the user with an image.
Prior to DX10, visuals were restricted because of limitations due to utilizing fixed function pipelines. The older cards possessed different processors for each major function. There was a processor for shaders, a different one for the geometry, and yet another one to deal with the pixels. So, if you were in an area with a lot of geometry, the geometry processor would max out and nothing else could be worked on by the graphics card until the geometry was completed, underutilizing the full power of the card.
In DX10, the processors are all string processors, with each able to perform any task. If a scene required a lot of geometry, the card assigned as many processors as were needed, while at the same time assigning other processors to handle shading or shadows, allowing the video card to use 100% of its processor power.
Another problem pre-DX10 was with compatibility. Cards claiming to be DX9 compatible weren’t always compatible with all DX9 functions, as the cards only needed to cover certain core DX9 functions with the rest as optional. With DX10 any card that is DX10 compatible from the budget releases to the $500+ models, is capable of performing all DX10 tasks.
The last major difference with DX10 is in how it handles memory. DX10 enables virtualized memory, borrowing memory from RAM when the card’s onboard memory is filled.
The Lord of the Rings Online was the first MMORPG to utilize DX10 technology. The effects on 
the game were visually amazing. With upgraded shaders for water, particle effects and lighting, and dynamic shadows, the DX10 version of the game increased the feeling of immersion. The world feels more realistic as seemingly random elements are placed into the nature of a scene.
A lot of the game takes place in an outdoors environment. With the DX10 version this environment appears more lifelike. There are fewer visual edges to shadows, and light flows through the environment far more naturally than with the DX9 version.