DUB-LON-USA and LON-USA aren’t the same offerings. One is direct, and thus comes at a premium, and the other is not. Other countries’ airlines do exactly the same. Go see how much Emirates or Qatar charge for one 6 hour leg to Asia (starting at their home hub) instead of two (starting somewhere else). Twice the flights, half the price.

If you are happy with a connecting flight, you have plenty more options at lower prices, but direct, much less so. So why should BA charge both at the same price, when they can get more for one of them? A smaller factor, is the higher taxes of exUK.

Personally I’m fine with this, because I’m paying less than a third for my Vegas flights from Dublin (via London) than if I started in London. And I won’t even have to fly back to Dublin. Thank god for this forum and the knowledge it provides.