Spring: HibernateTransactionManager handling multiple datasources

In the following piece of code (Spring 3):

@Transactional("txManager")
public class DaoHolder {

    @Transactional(value="txManager", readOnly=false, propagation=Propagation.REQUIRES_NEW, rollbackFor={Exception.class})
    private void runTransactionalMethod() throws Exception {
        dao1.insertRow();
        dao2.insertRow();
        //throw new Exception();
    }
    //...
}

• dao1 uses a session factory attached to datasource1
• dao2 uses a session factory attached to datasource2
• txManager is a HibernateTransactionManager using the same session factory as dao1

The code above works correctly in a transactional manner - in particular, when no exception is thrown, each dao operation gets committed (to 2 different datasources). When an exception is thrown each dao operation gets rolled back.

My question is: why does it work? Everywhere I've read I've been told to use a JtaTransactionManager when handling multiple datasources. I'd prefer not to use JTA. What might be the consequences if I leave it running under a HibernateTransactionManager?

Some more details for the interested:

Each datasource is defined like so:

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
    <property name="driverClassName" value="${jdbc.driverClassName}" />
    <property name="url" value="${jdbc.url}" />
    <property name="username" value="${jdbc.username}" />
    <property name="password" value="${jdbc.password}" />
    <property name="initialSize" value="${jdbc.initial_size}" />
    <property name="maxActive" value="${jdbc.max_active}" />
</bean>

Each session factory is defined like so:

<bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
    <p