I am thinking about what I am saying, my first draft of this post was a touch 'douchey' (if that's even a word...lol) my second draft started out with the logic escapes me as well but now that i'm thinking about it, i have this:
the coolant isn't sitting in the radiator, its FLOWING through the radiator. constantly, thanks to the water pump. so it doesn't have time to sit in the radiator like it would with a functioning closed t-stat.
i know i'm not crazy, my wife's car had a broken thermostat with it stuck open and she didn't tell me about it for 2 weeks. she just drove it with the windows down and the heater on because she thought i'd get mad her car was broken (woman logic... now that is tricky...)the car would stay cool when she was moving, but she would drive home on the parking lot known as the I 10 from down town to my place here in Ahwatukee off warner rd, stop and go the whole way and the car would overheat from not moving even with the fan full blast. this caused the car to crack the head, not 5 weeks after i replaced the head when it broke a timing belt.
its the opposite problem randysho is having if you think about it, just switch the word cold for hot, and switch the thinking of having the coolant sitting in the engine to heat up, with sitting in the radiator to cool down.