[wmf]

The problem with a generic codec DSP is how fast do you make it? Newer codecs often require twice as much computation as older ones, so do you make the DSP twice as fast as you need today and hope that's enough to run future codecs? Meanwhile you're wasting transistors on a DSP that won't be fully used until years later.

To some extent the PS3 did this; the Cell SPEs were fast enough to implement Blu-ray and streaming video playback in software and they made several updates over the life of the PS3.