Most, if not all games postponed today were due to fozen pitches.
A lot of the Premier League teams have undersoil heating at the grounds (Middlesbrough don't, but they have a large tent that they blow hot air through to keep the pitch i n good condition - the head groundsman claims that undersoil heating would ruin the surface), but it's expensive to install and so most lower league teams don't have it.
The final decision comes down to the Referee on the day and that's it. He's got to take into account the safety of the players and officials (very few people in football grounds give a monkeys about the officials). it'll only get colder as the day goes on so it'll freeze again and make the surface too dangerous.
OK eash? :-)