Why does the AP_VCHRBLD process update VAT and Currency Conversion row at a time when we are not usi

AP_VCHRBLD calls the Application Engine APVEDTMOVE, Section UPDQTY02, Step Step01 and section UPDQTY02, Setp 2, This steps selects and  sets the currency conversion rate. However we don't have international operation and we are using the one currency only. Why the program is designed to do row based processing for each voucher and update the currency conversion. It could do set based processing if the currency conversion rates are not set for the clients who do not have international operation and for the clients who have international operations it should do the row based processing. When we process 100,000 voucher we