Not sure that Infiniband has a place in a Hadoop cluster. Otherwise agree completely with the implied conclusion that SGI beats others hands down when it comes to Large Hadoop clusters.
There are a few lesser known players out there that come close to or beat SGI on density. PSSC Labs CloupOOP ( http://www.pssclabs.com/data-center/cloud-computing/big-data/high-density-hadoop-server
) comes to mind.
I think the bottom line is that the tier 1 server vendors still don't get Hadoop or don't want to lose the margin they are accustomed to in other environments. And don;t get me started on storage vendors re: Hadoop.