This is true. I recently applied for a job in the US and one in the UK. In the US, I got a ridiculously good salary offer. The UK job's compensation was maybe half what the US job offered. My cost of living is also lower than the folks in London, so it's just perverse no matter how you slice it.
I honestly don't think it will last, though. Economically, it just doesn't make sense. My recommendation to any of my fellow US developers: save as much as you can while the money is good.