It does seem that at least the part about there being two modes runs contrary to the actual plotlines. In the early episode "Dagger of the Mind", transporters were used for beaming what was supposed to be just cargo, but a live stowaway survived the process easily enough. In "Datalore", a cargo transporter moved Lore without killing him, despite the android supposedly being as intricate a piece of material as a human being is, and despite there being no story logic in specifically setting that transporter on "life-friendly" mode.
Also, many a plotline involves substances too delicate to be transported, while the transporting of humanoids basically never presents any problems. The few times there is a problem, it's deliberately caused by the resisting transportee ("The Hunted") or involves a major hardware failure ("Body Parts", "Our Man Bashir").
Perhaps a low-resolution mode does exist, but is very seldom used, and never as the default for cargo units. Or perhaps there only exists one resolution for the transporter to begin with - infinite resolution, as dictated by the pseudo-physics involved, and not subject to any sort of adjustment.