Tim, I think the question about what exactly we mean by 'institutions' is a really good one, too. I do agree that there are many differences between the different institutions you mention (government, NGOs, parties, corporations, etc.), but I think many of them are ideological or procedural rather than fundamental.
To clarify what I mean by institutions - let me start from the definition that my colleague John Hartley and his co-authors offer in their book Key Concepts in Communication (I'm working off the 1989 reprint I used during my undergrad days - it may have changed since then): for them, institutions are
Those enduring regulatory and organising structures of any society, which constrain and control individuals and individuality.
The operative words for our purposes here are 'regulatory' and 'organising' - and the way I would define institutions as I use the term (regardless of whether they're government bodies, parties, or whatever) is that they're structured collections of individuals which are organised and regulated - often quite strictly so.