The ou=People is a container that is usually used to store things associated with "people", such as user accounts; however it is by no means a hard set rule. An LDAP administrator can setup his/her own LDAP hierarchy and naming scheme, so if you may want to also ask this question to the LDAP Administrator of the external LDAP server you are connecting to.
It should be ok to change the base to be just "dc=example,dc=com" it just means that you are searching more of the LDAP tree, instead of just in the "People" container. This is really only an issue if you have a large LDAP tree as searches may take longer if you have to parse the whole LDAP tree instead of just a sub-container.
For a very brief overview of LDAP and to get a visual of what I'm talking about, see section 1 on
http://www.gentoo.org/doc/en/ldap-howto.xml