Hello Ciaran,
I think it might be nice if the client has a choice of how the content lays out. You mentioned a portal-like layout potential. I think a good content management system would allow an authorised user to associate the inital content to several other types of content.
For example a news item might have three pictures, or none. It might be linked to other news stories. It might be linked to a critical document that has just been published.
A news story with three pictures, just for example, would imply that instead of just designing one portal like template, you would design a more flexible system that could respond to the type of content.
Don and Lars can tell you about the best functional way to do these things. I've just had alot of experience with what clients want. Our people want alot of flexibility with the design, but thats because we are an extremely reactive bunch, used to changing our entire homepages daily. You might find that being in a Goverment situation, you'll need to change the front pages less often, but you'll get alot less minor hassle if you allow for more flexibility.
I hope this helps - it might seem a bit obvious :)
