Even assuming that this rack is located in an area accessible only to qualified personnel, this equipment should be enclosed for a couple of reasons. The first issue is, of course, the presence of dangerous voltage at the fuse protecting the primary of the transformer. In commercial sound systems, it is not unusual to find exposed voltage-carrying components (fuses, 70 and 140 volt speaker output terminal points, filter capacitor cans where the outside of the can itself is intentionally isolated from ground, plate caps on some types of output tubes in older systems which conduct as much as 1000 volts or more). All the more reason why this should be housed in a completely enclosed rack. Simply brushing against some of this stuff can really ruin a person's day...
The second issue concerns protection from fire. Some components, such as the SS rectifier to the left of the transformer (in the second picture)and some larger resistors in power supplies, can spark upon failure, hence the need for some type of containment. In some sound systems I have installed, I have recommended having a smoke detector attached to the inside of the equipment rack.
It is quite common to find microphone and line-level input cables in the same rack with heavy speaker output and power supply cables. Installers will normally go to great effort to route input cables well away from output and power cables by "dressing" them on opposite sides of the rack as much as possible.