You're  failing to take into account the electricity used by the people who did not generate a block. Maybe a better calculation would be 10minutes * power consumption of the whole bitcoin network / 50BTC = energy consumption for the creation of one bitcoin.

But this talk of energy needed for the creation of bitcoins is pretty irrelevant, considering that this process also handles all the transactions. So it would probably be more intelligent to compare the power usage of bitcoins to the total power usage of the current financial network, including the energy required to move coins and bills around, to power bank servers, to produce coins and bills, and so on.