FreePBX Distro support diferent flavors of asterisk:
Actually there is Certified versions of Asterisk 1.8, 11 and recently 13.
Why FreePBX distro don’t support this Certified versions?
From asterisk page: "Certified Asterisk releases have undergone additional testing and are made less frequently - typically two to four times a year. Certified Asterisk releases are generally identical to the Long Term Support release they are based on, save for additional bug fixes that were applied during testing. "
Certified asterisk are also robust versions with less regression bugs and Production Ready.