Yes but Slane Castle is in the part of Ireland that ISN'T in the UK.
They didn't play Wales, either, so I reckon they should play Scotland, Wales and Northern Ireland next time and everyone who lives in England can travel to one of those gigs, just as we had to travel to England this time. The Millenium Stadium in Cardiff is a great venue and Muse were here a few years ago (sadly before I became a fan).