Peadar
The Ulster was staged in Croke Park from 2004 to 2006 because of the fact that more fans wished to attend the game than could be catered for in any ground in Ulster.
Simple as that.
On a more general note, I read this site most days and, as a lifelong GAA person whose taken up supporting Derry City through mates in the past few months, I can honestly say that the twisted attitudes towards the GAA by some Eircom League fans are one of the biggest turn offs to me.