Although not desired, the default OFF settings exist due to an overabundance of backwards compatibility considerations. The default options are used only when the client API doesn't specify the settings when connecting.
Modern client APIs (e.g. ODBC, OLE DB, SqlClient, JDBC, etc.) all turn those options ON when connecting, with the exception of ARITHABORT which is ON by default with a database compatibility level of 90 or higher (SQL 2005). The implication is changing the default database options will have no effect unless you are using an obsolete driver or unsupported SQL Server version (SQL 2008 or earlier).
That said, there should be no harm in changing the defaults to the desired ON settings but I personally just ignore them.