Yeah, I'd love to see the said for London, Paris and say Brussels and Madrid. I'm pretty sure we'd have surprises (or maybe not ...)

This doesn't have developer salaries, but might be of interest. Edit: Forgot the link: http://www.numbeo.com/cost-of-living/

But precisely, that's the interesting part. For instance COL in Madrid and Barcelona are similar yet salaries in Barcelona are lower. It's kind of the point of the article, crossing COL data and salaries after taxes. COL alone in itself gives a hint but it's not enough.