No, they're not. My factory gauge sits at its "normal" indication with actual coolant temp being anywhere from 70 - 100*C. I haven't had temp any higher than that, so I don't know at what point the gauge will budge. 70*C is well below the thermostat setting, so 70 is not what I would consider "normal", but the gauge thinks it is.
This isn't just a Subaru thing. There are very, very few cars that have real gauges, and it's for exactly the reason that H-Dtech said (and that I've said in other threads).
As for the original question, unless you're going to tear apart the instrument cluster and put a new gauge head behind the existing gauge face I don't see any way to make the dummy gauge into a real gauge.