This finding is consistent with the results from WGHO.
(2.) Footnote 4 in WGHO: "Note that the setting we investigate assumes the existence of an authority with the power to implement an adopted rule." This assumption is not important for the focus of their investigation, which is rather what kind of rule will be adopted than whether a rule will be adopted and obeyed or not.
(3.) Margreiter, Sutter, and Dittrich (2005) found that homogeneous groups as in WGHO are more likely to reach an efficient outcome than heterogeneous groups in an equivalent situation.