Those are general device numbers. On top of how many might not be in use and all that, how many of those devices visit the site or sets if sites that were gathering the stats? And then only about 3/4 of a percent of those seem to have had iOS 7 beta. I don't think we can really easily tell one way or another, but given the rather limited distribution of iOS betas (and even accounting for a way to install the betas without being a developer and all that) there are just too many people out there with iOS devices who barely know how to change (or even about) half the settings that exist on them, let alone even know about betas and then even (assuming they would even want to bother and risk it) able to get them and install them.