The video @reanimated35 refers to is the one where a girl, with disabilities, is not allowed to go on some rides at Dreamworld. Not the full amount, but certainly none of the bigger thrill rides. However, apparently she is allowed to go on the same rides (or at least one of the same rides - a Disk-o, I think) at her home park of Rainbows End in Auckland, NZ.
Is one of those parks breaking their H&S rules? If a person unfortunately has disabilities, it may well be unsafe for them to ride particular rides (depending on the ride in question, and their disabilities). Yes, they may well have been on the same ride 99 times and everything has gone smoothly, but that doesn't necessarily mean it will on the hundredth time. Any remotely sane company should err on the side of caution, and I find the attitude taken by the girls in the video (and their parents for not correcting them, or doing any semblance of research before the visit - way to go, parents!) annoyingly entitled.
As for the person involved in the log ride incident, well we still don't know what happened. If he does have disabilities or handicaps which would have meant he was more inclined to stand up, well:
1 - were Dreamworld made aware of this, and if so why did they let him on the ride?
2 - if Dreamworld weren't made aware of this, why not?
3 - assuming he had a carer (and if not, why not?), why did his carer let him on the ride and not supervise him properly?
If he doesn't have any disabilities which impacted his thinking, then he was just being a prat. I do hope he's fine and everything, but Dreamworld owes him nothing when probably hundreds of thousands of visitors go on that ride annually and don't injure themselves by trying to show off.