This was essentially Ryanair's arguement, i.e. they won't be using T2 so why should they have to pay for it. But it was part of the deal with Aer Lingus and some of the US airlines who threatened not to move to T2 unless charges remained the same for both terminals. And you can see their side of the arguement as well, as it would've been uncompetitive for them to operate from T2 with higher charges while competing airlines were saving money operating from T1.
This vindicates my comments. Effectively, DAA built something that the airlines did not feel was attractive enough in terms of additional facilities and passenger appeal to be worth extra paying for. If T2 is so much better than T1, then pax would be willing to pay a small amount extra to use it - operating out of T2 would be a sellling point for the airlines. Clearly the airlines don't think that is the case. Therefore, T2 could have been significantly down-specced, made more affordable and been less of a burden on DAA.
It follws therefore that the airlines using T1 ARE subsidising those using T2, as the investment in T1 is nothing compared to the cost of T2. Aer Lingus being subsidsed by Ryanair - who'd have thought it!
MD