Of course they use it, those are update task FM (*) , at end of most if not all SAP transactions, once checks are successfully performed and the system has prepared data for update of database, call such FM in sequence IN UPDATE TASK and execute a commit-work. Did yu actually look at their source code?
Your suggestion is some "copy part of the whole transaction program" (copy every check and the preparation of dta...) so better use BDC, when no BAPI, IDoc or DIrect Input program available...
Regards,
Raymond
(*) Read some documentation like The Update Process and Transactions and Logical Units of Work / Database Logical Unit of Work (LUW) .