> Mostly financial transactions are done via append only ledgers, not updating;

Well, financial institutions will act as you describe, I presume, but lowly web shops will update 'shopping cart' and 'inventory' using the default settings of whatever DBMS the system came with.

Which is reasonable I guess, except that even with modern hardware, updating the same record in an ACID database has a surprising low capacity in terms of txn / second; if you have some popular item in your inventory (or popular merchant in your 2-sided shopping thing), you'll be forced to create multiple receiving accounts or other ugly stuff if you do the balance based transactionality.