[quote="abraxias"It's not really a "loophole" it is more likely that they're trying to compete in the Irish market and Aer Lingus fly the routes direct a lot cheaper than the carriers who fly out of LHR.[/quote]
Actually, they don't! I've priced them time and time again and before the ex-EU (including DUB) cheap fares came on to the market it was always cheaper for me to fly from LHR and with a separate booking on Aer Lingus. Until ex-DUB (and indeed ex-ORK and presumably-SNN) joined the ex-EU bandwagon (for want of a better word) EI always charged a fully flexible economy ticket of roughly €200 each way in addition to the VS fare. I always booked separate tickets!!
With the ex-EU fares, flights to and from the USA are still more expensive on Aer Lingus (and possibly the US carriers that use DUB and SNN because they know they can. For most people it is enough of a hassle getting to Dublin or Shannon without having the added inconvenience of LHR. OK, it suits me to fly to LHR as my nearest airport is Cork which only serves Europe. I'd rather fly to LHR simply because a) Cork is only 40 minutes from my home and b) I'm familiar with LHR and know my way around it so it is not daunting to me. Earlier this year, I flew DUB-SFO and loved it but the downside was having to drive to Dublin (and drive back after an overnight flight) as well as having to overnight in DUB before the outbound which was roughly about the cost of a return flight to LHR. The DUB-SFO was dearer than the ex-DUB fare for those of us in the Irish market and more so when one has to factor in a potential overnight stay and/or a rail or bus service to get to the airport.
To give an example - my boss goes to New York every year for roughly 10 days. Most of the time he books when the cheap buckets are gone because, unless he goes for a specific event as he is doing this year, he gauges when things are likely to be quiet work-wise. I mentioned to him the ex-EU fares (almost knowing what his response would be) It was as I expected; his brother lives in Ennis, a few miles from SNN so he can go the night before if he so chooses; the 9am flight on UA gets him into JFK at a time that suits him, especially if he is travelling on a Sunday; convenience rather than price is paramount - he doesn't have the time to go over to LHR even for an early morning flight to JFK. In other words, price is the secondary consideration with regard to flights going to USA destinations.