An engine without a thermostat will not neccessarily run at the same temp as with one when the engine is warmed up. As stated by andybird, without a 'stat, the engine will take longer to reach operating temp, but can run cooler or even hotter depending on the efficiency of the radiator. The thermostat even when fully open is an engineered restriction that does slow the flow of coolant down to allow it to reside longer in the radiator, allowing it to cool better.
Idealy, an engine with a 190 degree thermostat should run at 190 degrees as the thermostat cycles open and more closed. An engine without that thermostat may never reach 190 degrees if the radiator is efficient. It may even run hotter if the coolant can't stay in the radiator long enough. A high perf motor that wants to run hot will run where it wants to even with the thermostat wide open- no matter if its a 160 degree or 195 degree 'stat.
I think we agree however that thermostats should always be used