pcem/86box emulate an entire system (cpu, memory, bus, drives, ports, etc) while dosbox simulates a system below DOS. It may seem pedantic, but a simulation in essence "displays the right answer" while an emulator "shows your work". Especially with old games where devs were trying to squeeze performance out of systems, there are many timing or undocumented behavior tricks they used that a simulator may not replicate properly.
