[development] Postgres- For compatibility reasons we don't drop columns but rename them?

From the documentation of hook_update_N(): Dropping a column: MySQL: ALTER TABLE {$table} DROP $column Postgres: ALTER TABLE {$table} RENAME $column TO $column_old // For compatibility reasons we don't drop columns but rename them Why do we do this? What compatibility reasons? -- Neil Drumm http://delocalizedham.com/