Interestingly, SGI seems to be doing alright with their supercomputer business, such as UV. The market certainly shrank on them, but what's leftover doesn't look like commoditized or cloud computing will be able to compete it away any time soon.
I agree they made poor acquisition choices, but not that "expensive computing [is] over" -- it's just not the consumer market people thought it would be.
To be fair, it's not the original SGI anymore. In 2009 Rackable Systems (a cheap commodity server company) bought what was left of SGI and renamed their company SGI.
So, it's not quite the same lineage.
The new SGI does seem to have some nice gear, but I don't know how much secret sauce there is. I've never used it, but it looks pretty commodity to me. (Not that there's anything wrong with that).
I agree they made poor acquisition choices, but not that "expensive computing [is] over" -- it's just not the consumer market people thought it would be.