Rackable still impressive.
"....and a few other tier-one server makers that have only nominal market share in blades (you know who you are, Sun Microsystems, Fujitsu-Siemens, Hitachi, and NEC)...." Oh dear, the Sunshiners are going to take you off their Christmas card lists for that!
".....The fact is, if IBM and HP blade customers want to add a reasonable amount of storage to their blades, they have to rip out about half the blades in the boxes and buy storage modules that link to the blades....." Hmmm, but if you have a lot of blades in one datacenter then you're also likely to have a SAN, and HP and IBM (and Dell) are all better placed with storage offerings and SAN switch interconnects than Rackable. Even without the SAN, HP can offer storage blades and even NAS appliance blades inside the chassis, which with Rackable are either not an option or the customer has to build after delivery.
Still, Rackable still make very good kit, and it's beacuse they have innovated new designs that meet evolving customer requirements that they have not just survived but prospered (someone may want to point this out to a certain Mr Schwartz....).