Somehow everyone wrote to me about baldes. These are not the same, though. Blade servers were mounded into units of 4u, 8u, etc, they occupied a portion of the overall cabinet and still had to do "plumbing" for power and networking behind the chassis to the rest of the cabinet or to the rest of the datacenter. A full-cabinet blade rig would have multiple 8u blade units and some off the shelf units for networking, storage, etc. Yes, you could mix and match different components based on your needs, but that also meant that there were extra wires, cables, mounting rails, and more importantly - all these different components ran a mix of software that had to integrate using common denominator protocols and speeds.
Steve rightly mentioned the integration below, and I didn't put it in my message because I kinda assumed that we include software in this discussion too.
HP in 2005 had an army of programmers writing all sorts of firmware and software and another army of hardware engineers, too. They could have made an Oxide computer back then, and it would sell really well. But they didn't, and none of their competitors did despite this being an obvious product (in hindsight), an THIS is what I find interesting.