Does TRANSACTION/COMMIT/ROLLBACK only work on certain MySQL engines such as InnoDB? Are transaction functions only relevant for particular database engines on MySQL, or are transactions supported under all MySQL engines, including MyISAM and InnoDB?

someone says here that transactions only work in some tables types
The only storage engine ("table type") that supports transactions with the standard MySQL 5.x distributions is InnoDB.  MyISAM and the others do not support transactions.   

http://dev.mysql.com/doc/refman/5.5/en/ansi-diff-transactions.html