If it isn't readable, that is what is desired. Or, the application could check for currency formats but it is not necessary. It all works. It is not complex. It could be very onerous for companies that have pre-existing XML data and applications.
Elements contain significant data.
Attributes contain significant data. My job is to supply solutions for encrypting that data if there is a need for it. And, there is a need for it. Restricting the flexibility of business applications is not a good way to simplify. Attributes were designed into XML to be used.