Oracle OLAP cubes can be queried using either ODBO and the MDX query language or ODBC and the SQL query language.  Bud Endress from Oracle does a good job explaining the difference between "Excel and OLAP: ODBC vs. MDX".  From an Excel point of view, there is a real difference in functionality and performance of how you query Oracle OLAP cubes.  Since Excel Pivot Tables natively understand how to issue MDX queries to OLAP cubes, it just makes sense to use the MDX query language for Oracle OLAP.