I have to agree on the hot plug comment here. These aren't processors, they are full computers on a small board, and they connect into a backplane only for power, RJ45 ports and a serial port to the integrated managment board. Show me a server that is completly hot plug. The Tandem based non stop systems have many hot plug components, but would fail if you pulled all their power. Same concept here.

And if you look closly, the removal buttons don't have the same color as all of Compaq's hot plug components. Probably a good idea, though I still see people trying it.

Oh, and most people will see one component as a single point of failure, the enclosure. Everything that needs to be is redundant (cooling, power, network), so there is little that can bring all the blades down at once. The "backplane" that all the blades plug into is only made of connectors and circuit board wiring. Absolutly no chips of any kind are on it, so the odds of it failing are huge compaired to the other components.