B737NG Fire Detector Fault

[Ziggy]

Going to my QRH recently and noticed the following in the fire section:
For the APU Fire Detector INOP, it says: shut down APU and CAUTION, do not operate APU anymore because a fire would not be detected!!!
For the Cargo Fire Detector Fault and, more importantly, for the Engine Fire/Overheat Detector Fault it says: the detection system in one or both of the cargo holds/engines is inop....
Period, end of checklist!!
This seems a bit odd to me. Is a running engine with an undetected fire less dangerous then a running APU with the same problem? Consistency would suggest to shut down the engine and land asap, or at least land asap on both engines.
What if you get an engine fire detector fault indication in the cruise with 2 hours of flight to go to your (engineering equipped) destination and ten minutes away is another engineering base.
Continue to destination or divert??

Greetings, Ziggy