Pixel Shaders > 3 are for directX10 and above. This would gray out a lot of customers that would be able to play the game with their video cards.
Pixel shader 3 is not found on a good amount of cards that can still play EQ2, but it will be wonderful to have it implemented I guess as an option (if that's what they're planning on doing).
Here's a pixel shader run down....
http://en.wikipedia.org/wiki/Pixel_shader