OK .. I will attempt to give this a bash
CMS - Content Management System
when a client wants a CMS system they want something where they can control and categorise their data easily..
Create a document - add images to the document often via a WYSIWYG manner
align text around images etc
They would then like to be able to place this data into the category of their choice so that the category TRAVEL would have all the articles created for this category listed under there
Each category should open to its own presentation page
It will also allow for the ability to change and manage the content by the various users
so this comes to user management and the ability for them to be able to modify said content easily
here is an example of how I would like the data to be displayed
Global-Travels - News
personally I would like to have achieved this via vBdrupal however I have not made the time to develop that aspect. vB4 is most interesting to me but can't comment on it.
and yes, I use vBadvanced extensively but certainly not as a standard CMS
I hope this helps put across why I don't consider vBadvanced as a CMS as it truthfully is 'lightweight'
then there is always using Wordpress as your frontpage and making it a CMS while using the vbulletin bridge