Curt B, Yes, because all the oil on a full flow goes from the pump to the filter there has to be pressure relief valve. When the filter becomes blocked or the oil is very cold, the bearings would starve or the screw on can could explode (seen it) due to excess pressure.
Some engines have the spring loaded valve in the block, others use filters with internal relief valves like the one you described. But at normal operating temp and a reasonable clean filter, all the oil goes through the filter.
