Uhh, well it's probably pretty high. Considering their adoption rate for new software is sitting somewhere around 95%. iCloud backups default to on - just like automatic updates - when the user sets up their phone. Not to mention most Geniuses would ask to turn on iCloud backup when upgrading the device for convenience.
It did have iCloud backups, but the latest was six weeks prior. The FBI requested the iCloud password be reset, which prevented a new iCloud backup they could have subpoenaed.
