DDS can be superior to PCX even when it comes to gradients. Even for static effects!
This is an exaggerated example:
Base map:
256c PCX

DDS

Well, but who needs this ammount of colors?
Probably nobody, but some of my effects look better as DDS than as PCX. Not very much though.
I'm not sure about this, but I think DDS has one big advantage over PCX. The way 8-bit images get resized in-game (distance-wise) is just ugly.
I think it's like this:
Base map:

Resized PCX:

Resized DDS:

So for animations DDS is the better solution, because animations often have many different colors and grafients. And i.e. shockwaves will look better when you're close to them.