"new version" is about 5 years old.
forward only : it is the easiest way to implement. It is easiest to implement a Queue(FIFO) rather than a deque or linked list. Since the JDBC driver has to read the record from the DB, it can make them EASILY available to the ResultSet reader FIRST COME FIRST SERVE.
Later on, they realized that some desktop applications and some rich web based apps might want to scroll forward and backward without having to store the intermediate representations, they decided to implement it.
Then came the updatable ResultSets where you can update the columns/rows of a ResultSet.