Is this the same method being used on you site?
http://blockexplorer.com/q/totalbcI hope you can consider providing these service to function as an early warning system for the bitcoin network.
It's not.
The value returned with the SQL is now actually less than the "ideal" number, as some miners have thrown away block reward BTC. I might make a /q page for it eventually, as the difference is interesting.
It only one block (#124724) that doesn't balance this way so far. He was intending to throw away 0.00000001 BTC but accidentally also dropped a fee of 0.01 BTC so he made 0.01000001 BTC in all disappear. Of course its not really any different effect than someone losing their wallet.dat file. The value is gone either way.
For reporting purposes it could be credited to a special "lost" account address.