Could this be because of the change of government? The new government is dismantling all sorts of other central government internet projects - perhaps the data providers who were being pressured into making their feeds available are spotting a change in the political climate and a chance to keep the profits in-house.
I'm not so sure, I think it more a case of lots of these APIs and open data projects exist as "side projects" and do not receive the full backing and resources of the department/organisation.
I followed up the story of TFL and it turns out that the API stopped working because of a security patch that was applied, rather than more sinister reasons.
I blogged about this recently http://andysinclair.wordpress.com/2010/10/25/your-api-killed... as I was very annoyed that TFL (London's transport network) disabled one of their APIs which stopped 2 very popular iPhone applications from working.