It's a bit more involved than that. It is x.500 compatible for database structure, and LDAP itself it simply a database access method/protocol, so saying that AD is just Microsoft-LDAP is a bit unfair.
It's a bit more involved than just that. However I dunno if you could use LDAP in let's say Linux to do it...all the information to do it is open, so I don't see why not. SAMBA has been using Microsoft's SMB for a long time for cross-compatibility.
For a large network, I'd rather have AD.
Actually, Active Directory is
a Microsoft-fied LDAP network. Here's the Wikipedia description:
Active Directory is an implementation of LDAP directory services by Microsoft for use in Windows environments. Active Directory was released first with Windows 2000 and saw some revision in Windows 2003.
It's essentially LDAP for Windows, well, it's a MS-Centric LDAP for Windows. For a large network running a pure Windows platform, yes, I'd rather have AD. But my network comprises of Linux boxes, so I'd rather have LDAP and NFS.