The problem, as I see it, isn't the dodgyness, it's that the Lib Dems needs cover to back a vote of no-confidence. A vote of no confidence in a government you're part of is a big deal. If they vote no-confidence on the grounds that Cameron had meetings (even meetings) and no hard evidence, then the only thing Cameron needs to do to absolutely end the LDs is to demonstrate how Labour also had meetings (News Intl were behind Labour in all the Blair elections). Heck, Murdoch might just do him the favour and dump the minutes himself on the way out.

Also, LDs are in plenty of trouble with their base. They swallowed tuition rises but are willing to fire the PM over being too nice to Rebekah Brooks? Tuition affects pretty much everybody who will go to university or who wants their children to go to university. Loose ties to repulsive, illegal behaviour at at newspaper everybody already knows to be the scum of the earth affects comparatively no-one.

Finally, Coulson was working for Cameron when the coalition was set up. How does it play to be fine with that, and then suddenly be against some meetings on a vague principle?