No rarer really than when they were in Brazil - 3 or 4 screenings a day. I think London 2012 had some breaks within the coverage too rather than handing over from one presenter to the next. More than that though it was the biggest event the BBC had ever coverage and as such should have been marked by presentation.
Anyhow, that's an 8 year old argument from a time when we felt our countries future was bright.
I preferred the internet when it had a sense of humour.