The numbers in the table below are for the four championship years between 2008 and 2011. They are based on just over 60% of the senior championship games played in those years because the other 40% of games were played on neutral ground. Croke Park features prominently in the games held at a neutral venue. All later stages of the All-Ireland series tend to be held in Croke Park. This is a neutral venue for all games not involving Dublin.
Connacht is an outlier. One of the reasons for this is that New York and London play in the Connacht championship. Despite London's heroics in the 2013 championship, it would be fair to say that these teams are the weaker teams in the competition. To help foster the game in these parts of the world, the GAA allow London and New York to play their first games at home. In the period 2008-11 both teams lost their opening game in each year. If these games are removed then the winning percentage for home teams in the Connacht championship is 50% and the away team wins just under 44% of the time.
For the record, Dublin footballers have an impressive 81% win rate in Croke Park over the 2008-11 period. It would require a more detailed analysis to say how much of this is due to them being a good team and how much is down to home advantage.