Even Apple, which became the unlikely last of the Unix workstation vendors, was disrupted by Intel (and moved from PowerPC to x86 for a while). Ironically, Apple is now the very last Unix workstation vendor in existence.
Apple abandoned both intel and Nvidia (not to mention AMD/ATI) which is interesting. Apple seems to be vertically integrated like IBM or SGI - but better at differentiation and at locking in new customers.
Apple seems particularly good at differentiated product design; their devices often just look better than the competition and seem to offer a better user experience.
(That being said, SGI's designs look pretty cool too.)