this is what i though also but wasnt sure.Completely wrong me thinks...
Inlet manifolds are matched with the head, what good is it when half of the process is done?
In your case there's no matching...
http://www.angel-works.co.uk/service_inletmanifold.php
Quote.: "The most typical level of modification starts with the matching of all faces to its corresponding component."
So there you have it...
ye you have sort of got it wrong but not completely.
in simpleman terms
The inlets are boshed out in the factory and are slightly smaller than the head as standard and have some minor imperfections in them. getting them matched i.e ported etc, means you will have better smoother airflow delivery as such.
hope this helps.
For the record i will be selling a set of these when i convert over to ITBS in approx 2 weeks.