Although this reference nicely explains the origin of the diffraction pattern on the JWT images, it does not explain why the spikes seems to extend much farther then in the Hubble images. My hunge is that the JWT succeeds much better to gather all the light into a real point which makes the primary diffraction pattern stronger too.

While this is very important for scientific work (easier to see planets!) it is less appealing to the eye. Also note that some JWT images have some faint blue streaks which in effect are diffraction spikes from bright stars outside the field of view.