[ascl_]

The refresh rate is not related to the ability to decode a particular format. How the image is taken from compressed format to something that can be displayed is what you are talking about when you talk about decoding on the CPU or GPU. Once that image is decompressed it is displayed on the screen at a certain refresh rate (well a stream of images, not just one).

So, to flip it around, ivy bridge wasn't able to accurately use a 23.976 refresh rate, regardless of how the images are decompressed. Haswell can.

EDIT: Bah, beaten to the punch by lmyllari!!