How can the resistance of museums to the participatory web be explained?

Mia Ridge, a database developer for the Museum of London, asks some interesting questions on her blog Open Objects about how museums and cultural heritage institutions relate to the ‘participatory web’ (web 2.0, social networking sites, user-generated content etc).
Mia’s (perhaps not very unsurprising) impression from speaking with colleagues is that museums are pretty conservative in this respect. But also that there may be differences depending on what kind of institution we’re talking about. (Maybe art historians are more resistant than social historians?) She also wonders how the resistance to the participatory web is expressed. Is it active or passive? And a lot of other interesting questions: “At this point all I have is a lot of questions”.
Note that the resistance Mia has found doesn’t seem to be against the digitalisation of collections or web-presence as such, but specifically against the participatory web.
These are interesting observations, and I wonder: Can this resistance perhaps be understood in terms of an opposition among curators against a perceived profanation of the sacred character of the museum? In the same way as Wikipedia and other user-generated content websites have been viewed with skepticism from the side of many academics — not just because they may contain errors (which encyclopedia doesn’t?), but also because it is a preceived profanation of Academia. (For earlier posts about profanation of the museum as a sacred institution, see here and here.). Any ideas?
PS (25 February): Mia answers today, here.