Hit the nail on the head.
Unfortunately, they try to make effects that aren't so demanding on computers. Keeping minimum requirements as low as possible means more money for them.
However, I'm sure in the next couple of years they will change some, for example, with everquest, they put out a new spell effects system that looked great, but was optional. Same for the newer models.
I think that the programmers like eye-candy as much as we do, and most of them have a desire to make THEIR game better. I alos think that alot of times little things like that happen in their spare time, so it will take a while for it to get finished/submitted/approved/tested/added, etc.
But it is a nice though, definitely.