I went to OpenTech 2013 and by far the most packed session was Peter Hicks' (Poggs) talk about open rail data[1]. I worked at Rockshore, who maintain the Network Rail datafeeds, and I remain grateful but astonished at how passionate people are about this data.
The huge London-centric contingent of developers likely have to endure a hour-long train trip twice a day, every day. That's basically a month of their life, every year, spent in trains. Obviously they'd jump at the opportunity to improve their life, if given half the chance.
[1] http://www.opentech.org.uk/2013/audio/streamC/session4.mp3