Blizzard never releases any info on store sales. But the Armory can give a reasonable estimate to anyone with the ability to scrape the data.
MMO-C, please tell us what percentage of active players (or something similar) have store mounts and store pets, along with perhaps some other items like SoR and RaF mounts. We would find it interesting, I bet, and some actual light would be shined on this otherwise dark corner of Blizzard's business practices in the process.