I, too have noticed this behaviour of dbaccess for DDE and DML.
Apparently, dbaccess precedes DDEs with begin keyword. If you need the dbaccess to prompt you for your DML for Commit/Rollback, you need to start block of SQLs with "BEGIN ;" sql statement in the dbaccess -> Query-Language option.
You will agree a point that DDLs are not used on every day basis, hence creation of an object are done after a long planning, strategy and diligence. As you know in DB-Access after the completion of operation it prompts for Build & Discard "ring" menu, if you select Discard, you may have noticed that, it does not prompt for Commit/Rollback, But only ask for it if you have opted for Build the object prompt.
This way It gives an opportunity to reverse your effects in case if you wish; since any such change may backfire if not logically proper to a domain requirement. It's your last resort to keep the original object unaffected.
By the way, dbservers supports DDL statements with transactions. Like:
create table tab1 (f1 char(1));