No-one was saying it is there to replace SANs did they? The purpose of stuff like Fusion-IO is to get a massive performance increase for certain applications.
SANs and SAN attached RAIDs are great workhorses but it doesnt necessarily make it the best fit for all application.
You are also making a nieve assumption that the only way to get redudancy is through storage. There are other ways. Applications like Casandra for instance, manage redudancy by having different nodes each deciding how often and where data is replicated. This provides massive scalability for both performance and capacity. In fact, using a SAN for such a system creates an unnecessary amount of complexity and greater chance of failure.
" Will it supplant them? No."
So this statement is Yes for certain applications but No for general use.