Would would the need for "specialized gear like infiniband to reduce intra-node latency" be limited to parallel databases? (I assume you mean "inter-node"...)
Well, replace "parallel databases" with your favorite term for the parallel databases that fall outside NoSQL (VoltDB, Exadata, shared MySQL, etc). My point being that the alleged need for high-speed interconnects is orthogonal to SQL vs. NoSQL.
But it's not. Because SQL databases (strictly speaking any requiring strong consistency... which is mostly RDBMSes) are highly latency sensitive, where NoSQL databases like Cassandra design around that by saying "hey, you could not see the most recent write for a few ms, unless you request a higher consistency level." And most apps are fine with that. As a bonus you get multi-datacenter replication with basically the same code, another place most RDBMSes are weak.
It's a classic design hack -- redefining your goal as an easier problem.
Oh, I see what you're saying. Yes, the interconnect is orthogonal (although you could argue that strong consistency requires more complex protocols like 2PC so interconnect latency becomes critical).
