A significant factor in this was that it was the first system that used a standardised hardware bus implementation, the Omnibus, which obviated the need for complex backplane wiring - you simply slotted in a set of cards to do whatever you needed. It is the direct ancestor of the expansion buses in todays pc's.

These racks are part of the largest pdp-8 configuration I've ever seen, from the control room of the Tornado hydraulic systems test rig at British Aerospace, near Preston. There were only the two cpus shown above, but a total of about ten racks of equipment, more than half being custom built control systems for the test rig- DEC racks, but no DEC contents. I left most of that in place, as it was so specialised it had no meaning without the rig it controlled... and that weighed hundreds of tons, and took up a fair sized hanger, so I decided to leave it behind. I contented myself with removing the cpus and their peripherals, which included more lovely DF32 fixed head disks - used as substitute for expensive core memory.
 

Here are some of the bits I removed:
 

     

All this lot is in storage awaiting assesment - should work ok, but I couldn't power it up on-site to test as they had started dismantling the control room and the power was off.