Some of the reasoning is explained or linked to in MGNLLDAP-39.

Using the Enumeration methods (hasMoreElements(), nextElement()) hides any exception; while this satisfies many scenarios, by simplifying the problem, it doesn't solve.

Using the specific NamingEnumeration hasMore() and nextElement() methods make problems more prominent, thus reducing the probability of side-effects or inconsistent results.

http://download.oracle.com/javase/jndi/tutorial/ldap/referral/jndi.html
http://download.oracle.com/javase/1.5.0/docs/api/javax/naming/NamingEnumeration.html