I can't help thinking that the Vince Cable story is a knock-on effect of Wikileaks.
The biggest effect of wikileaks may not be either the secrets that it tells, or even the fear of the secrets it may yet tell. It may be the secrets that others tell, because of the feeling, "when all that is already in the newspapers, why am I keeping X a secret?"
Is it a breach of confidence to secretly record what an MP tells a "constituent" that he has never met? It's pretty thin... it is just a politician talking to a voter with no extra qualification; if he tells one voter something, what right does he have to keep it secret from other voters? But nobody did it before.
And, of course, the current story is based not just on the Telegraph's secret recording, but on a leak of that recording -- the Telegraph, perhaps for business reasons, chose not to reveal Cable's claim to have "declared war on Murdoch". So someone at the Telegraph leaked it to the BBC.
I rather suspect that norms as to what is publishable and what isn't have changed suddenly.