The intranet web site I manage for our company (of about 35000) is now a decade old. Immediately after it was set up in 2001 the portal became a hit and was touted as a breakthrough innovation for employees engagement. The content owners had remained always Corporate Communications ( I am from that) but the platform management for first first 5 years was outsourced directly by CC through third parties but later IT department created a platform and made CC move intranet website to that .
There started the problem.
The popularity declined and content quality deteriorated as less and less of employees started coming forward to share and contribute, mainly because IT Department created platform was purely built on concept they thought was technologically manageable by them. Obviously their thrust was on 'convenience of maintainability' not 'user-friendliness'.
The soft-information architecture for the distribution of content which CC felt best meets organization needs was not 'fitting' into hard - technology they offered. Loser was the organisation having unpopular Intranet, even forcing some of the geographically separated divisions to start running their own intranet thus defeating the very premise of cohesive organization wide one portal as was mandated initially.
The intranet portals must be owned by Corporate Communications as they are the ones delegated to handle communication best suited to management's perception and needs. Also the IT should manage the back-end platform and provide 'hosting' services to CC to run the portal . What would be IA, 'look and feel' of the website and how content would be sourced and hosted is all what should be job of CC.
IT , as service provider, should provide best fit required for meeting needs of CC not other way round. CC may create channels/subsites ( moderated/or independent ) delegated to various other divisions( operations, HR etc) for meeting overall mandate of management or may run part or whole centrally . IT should strictly work to meet user requirement of CC as managers/owners for the Intranet Portal.