The *CPU* is much faster. However, at least in the old days, the *GPU* was very primitive, and did not provide any assistance, so your average Pentium II had to do all the work in order to play a video.

A much simpler example is MP3. With a 486 you basically could not play MP3, you needed at least a Pentium II (or an overclocked Pentium, but those used to burn through the motherboards).

Your average Nokia feature-phone plays MP3 without a hiccup.