Truth be told, they're the same thing. It's probably just built in like that to follow a format, making it easier to access. You can deduce that there's no difference between #hdmi_force_hotplug=1 and hdmi_force_hotplug=0, as the value of hdmi-force-hotplug can only be either 1 or 0. You'll have a hard time deducing that #config_hdmi_boost=4 can actually have five values (0, 1, 2, 3, and 4) instead of just two (0 and 1).