That's not completely true and exactly what this article seeks to discuss. If you introduce a failover clustered instance of sql server into the AO group there is still shared storage and a SPOF somewhere in the cluster.
With SQL and AO, give me a scenario where some shared storage goes offline and it renders your data unavailable.
If the quorum disk goes offline, who cares? At worst the cluster loses quorum and the default behavior is to leave all resource groups in the cluster running. They simply remain frozen on whatever node they were on until quorum can be reestablished and the cluster service can be restarted on all the nodes. In the meantime, the AO listener switches connections over to a replica in a matter of milliseconds - automatically.
With RAC if your shared disk goes offline for even a millisecond, you've got to restart the entire cluster. That is a time consuming, completely manual operation. I've never had a situation where I could simply restart CRS, or even just reboot the nodes. They need to be completely power cycled or CRS wont start correctly. That process takes 30-40 minutes per node, and they must be power cycled one at a time.
When this happens at 3am I'd much rather let AO switch connections over to a replica automatically while I sleep, than get woken up and spend the next hour or two bringing the RAC cluster back up.