Puck:
You have probably reason, My furnace of heating have a 100A breaker and Main is 200A...
I have 20KW element heater inside my furnace. 20,000 / 240 = 83.3Amp
Other exemple: my Refrigerator have a 15A breaker, but his real load is 4Amp
So Truth, each circuit breaker was only installs to protect each one of their wire, and we can't adding all breaker value to know a total capacity but just Theoretical.
Now, we can't forget that our Main Breaker 200A are installed to protect our Main Wire connected to our electricity Company distributor !