It does, because although each of the board's DC-blocking passive capacitors actually isolate every active transistor device circuit, when a capacitor fails from high-voltage overload it fails short, and can then pass the DC voltage it is supposed to block into the diode or transistor, killing its junction; whereas an optically isolated circuit fails open and cannot pass DC (or signal, either), thus preseves the devices it is protecting from stray DC surges. But optical AC signal transmission is far more expensive to achieve than capacitive DC blocking, so no economically prudent manufacturer will have more than a few such optically isolated interfaces.
Anything of higher voltage or current operation will be protected by a fusible link, not an optical, capacitive, or diode-linked fail-safe element. BTW, the brown rectangular devices on the USB bed are MLCs--multilayer ceramic capacitors. These capacitors are made of essentially barium titanate insulator material which has a very high dielectric constant, making them able to store a thousand or more times the charge that an air gap would provide.
But the area is so small that a lot of internal plates are needed to store very much charge, and the gap between the internal plates is therefore so tiny, that very high voltages between the plates cannot be tolerated, else the dielectric material isolating the plates will fail and the capacitor will short out.
The devices you see pictured are commonly used in circuits that only operate at a few volts. These capacitors cannot store enough charge to be very destructive, so they are much less dangerous than, say, an electrolytic capacitor designed for 250 volts and 2,000 microfarads (for a camera flash), which can knock you on your fanny, and when held in one hand with the charged lead touch by the other hand, might give enough of a jolt to stop your heart as the current passes from one hand to the other across your chest.
The capacitive USB circuit you see is not likely to store that kind of energy.
If I could understand your post perhaps I could apply for a mini degree in electrical engineering :)
Thanks much for the explanation.