Just a wild guess, but it's possible that since Zuckerberg has a keen interest in VR that he's basically taking all of the fun vision / strategy parts of being the Oculus CEO and leaving Iribe with the slog.
I think you may be correct but got there the wrong way. From the lateral movement I think Iribe wanted to stay product focused instead of business focused and moved laterally within Facebook to do that. Whether it was from Zuckerberg or just the normal evolution curve of a startup CEO from productization to monetization can be debated - but the move to stay within Facebook seems to indicate it wasn't Zuckerberg's fingers (or handcuffs).