Australia Zoo could well have established themselves as one of the breeding hubs for gorillas in the region has the plans come to fruition. They got to the construction phase (excavation of the moat) in 2007; but shortly after, the plans were changed to build ‘Bindi’s Island’ which is widely criticised by ZooChatters for lacking any sort of cohesive theme.
You’re correct that Australia Zoo just have Ring-tailed lemurs. Lacking great apes is one thing, but they don’t even have any of the numerous small monkey species housed at Wildlife HQ. Wildlife HQ have Hamadryas baboons, Siamang, Northern-white cheeked gibbon, Night monkey, Black and white ruffed lemur, Ring-tailed lemur and numerous small monkey species (tamarins, marmosets etc).