True, later versions of Oracle allow you to treat a flat file as a
database, and of course SQLLoader is also available to load flat files.
 However, the need JRower was written to address is where you want to
give the end user the ability to "upload" their spreadsheet to a
database through a friendly user interface. The user interface does
some data validation before accepting the data.  Additionally there may
be many user's who's spreadsheets may only be a sub-set of the database
rows.   In the "Bowling Team" example each team captain uploads only
the data for his team to a database of all teams.  The end user can't
replace the entire database at will, but can only execute limited load
logic that has been setup in advance by the programmer or DBA.  The
load logic is saved in  XML files, that can be added or edited without
deploying new code.
The point of JRower is to give Java programmers, in the words of
another poster, "a SQLLoader-type API", that they can use to create
user interfaces to allow end users to "upload" their spreadsheets.