That is 100% up to the individual artists. For example, all of the presets we designed with Synyster Gates from Avenged Sevenfold are available for purchase on his store. Similarly, we'll be releasing the patches I designed with James Valentine from Maroon 5 soon. The factory Petrucci rig preset is very similar to the preset JP uses live, etc. etc. It just depends on what level of publicity each artist is comfortable with in terms of their sounds.
I only see cab packs for sale on Synyster's site, no presets.