Are you sure the transformers are really paralleled? Most often (around here at least), you'll see small strain insulators inserted in the two hot wires of the secondary bus to break it into independent sections, each fed by a single transformer. Or there may be two secondary insulator racks on a pole, but the transformer is only connected to one of them. A secondary section may physically span several poles, or it may only serve the houses connected to one "maypole", but in either case it's electrically separate (except for the neutral).
Secondaries *can* be paralleled or "banked", but I think it's pretty rare in aerial distribution. I believe Detroit and someplace in southern California are some of the few places that do it.
In contrast, urban areas with high load densities often do have such "network" systems, usually underground. These feature breaker-like devices called "network protectors" to isolate failed transformers from the interconnected system.
