The general route for updates is for Fairphone to send it to carriers so they can confirm it works, once Fairphone get confirmation it works it is then pushed out via those carriers who have accepted it as being viable, hence the delay that some carriers/network users experience.
.Together with our partners, we test the software before its release, and in some instances where a software update might result in some problems for users on a specific network or in a specific country, we prefer to delay the software release for that specific customer base and fix all the potential issues before making the software available to everyone.