Actually BAS is the web replacement for the former BlackBerry Manager.
In the good BES 4.1 days, my BES configuration is like this:-
Computer 1
-----------
Remote BlackBerry Manager
Computer 2
-----------
BES Core
Computer 3
------------
SQL 2000 SP4
Moving on the BES 5.0, my configuration is like this:-
Computer 1
-----------
BAS
Computer 2a
-----------
BES Core - Primary BES
Computer 2b
-----------
BES Core - Standby BES
Computer 3
------------
SQL 2005 SP3
I like to chart this picture, it's so much easier to explain!