My airline also has a very tight fuel policy. The captain is responsible of course, and can add additional fuel. But the trend is monitored and if he/she falls outside the box it will be looked into (I know of only two cases in the last ten years though, where people were asked to explain themselves).
One thing I don't understand in this, is the fact that we never discuss unusable fuel. If we land with 45 minutes fuel (not rare at all), we always assume that it is indeed 45 minutes, while back in my little old cessna days there was a quantity that was considered unusable. In our FCOM's it does mention high pitch angles and the fuel pumps being layed bare causing further alarms, but that is about it. I can't imagine uninterrupted fuel flow all the way down to zero.
Question for me has always been, why is there no unusable fuel? And if there is such a thing, why isn't that then automatically added to your minimum 30 minutes (in order to make sure you have at least 30 minutes!).
Greetings O.