Short Depth Chassis are somewhat of a limited market. Most standard 19" server racks are designed for servers that are 20-30" in depth. Datacenter racks are typically 30+ inches deep to accomodate a deep server and all of the associated cabling. In contrast, short-depth or A/V racks are typically around 20" deep, which limits the type of equipment that can be installed. The market for these servers is more limited, as most datacenters are looking to achieve density in their racks, and due to hot/cold isle placement, it would not make sense to locate servers on both sides of the rack.
We have also put together a few other resources on Short Depth Rack Mount Equipment, including:
