Now this is purely speculation and idle curiosity but I'm wondering if all is right in the Cameron marriage. I can't remember the last time I saw Sam Cam 'on public duties' but perhaps she has been and I've just not seen her? Now I've read this (Daily Mail link) and it just screams at me 'My wife is refusing to have anything to do with me so lets hide that by keeping all other wives etc at home'. Or AIBU and clearly their wives would distract them from talking about tax etc? 
The ongoing strain of living in Downing Street must be huge and when you add in to that their grief for their son I think that's a receipe for danger to any marriage.