I think you have a very valid point here, when you remove them from the LDAP group they should be removed from the list (More of a smart type technology). I think that LANDesk has a similar view but it's just taking them a little time to move that way. If you are working with policies It seems to me that LANDesk does have an option that does this. You can check this out and let me know.
When adding your LDAP group to your task a small window appears with three options. 1) User Objects 2) Machine Objects 3) Group Objects. If you select either user or machine you will NOT get the dynamic list that you were talking about. It is only when you select the group objects check box and then you will have the dynamic list that you are looking for. I hope this helps.
Again this is only for Policies.