So, what's Dublin got to offer that Manchester doesn't on a route like this?
A traffic profile that is representative of the fact Ireland is a sovereign state, Dublin is the political and commercial capital and, according to the 2010 census in the US, about 38 million people in the states claim Irish ancestry.
Result - a more balanced two way passenger flow with a greater premium mix.
Of course, the tax and pre-clearance is a further advantage too.