You have a good point there Greebo, at least in regards to the Aussie species, most are ground dwelling and I can see that it would be safer in respect of those species to have top opening viv's.
I have worked with many venomous species in the UK and have always had side opening viv's, but several of the species I worked with were arboreal, alot weren't though, and apart from Zoo's, no one else that I knew kept Hots in top openers in the UK.
The reason I ask is that I saw a program the other day regarding Eric Worrel and ARP and they showed all his viv's as side openers, maybe it's because it's easier to keep alot more snakes in a smaller area, where as top openers restrict how many viv's you can have because you can't stack so easily.
Is there any sort of State requirement that insists on one way over another?