All gas appliances need a regular that is designed for its own BTU requirement. A 30K BTU gas grill regulator will not be the same as for the 86K BTU grill. Regulators for gas grills and burners/fryers have a required safety device that shunts down the gas flow. It's shunted, not shut off. When a sudden drop of gas pressure past the regulator occurs, the gas flow will be mostly be reduced to a pilot light level. Before this safety requirement, (those old grills that used the left hand threaded fitting), if the hose accidentally broke loose, or was burned and melted apart, the hose would turn into the blow torch. A few homes burned down that way. The new regulator (about 1996 or so) will close off the flow and the flame would be reduced. A small gas flow is wanted so the flame does not travel up the hose to the propane tank or other source.
It's all about safety. If a plumber created a manifold to just use one regulator and something happens where someone was burned or injured, your lawyer will go after anyone that touched that pipe. Sylvan, the first expert master plumber to respond to your post, is an expert witness for plumbing and heating disasters, usually where someone has been seriously burned, scared for life, etc., from scalding hot water.