What do Bruce Schneier, Mark Chu-Carroll and Paul Graham have in common? They're all bloggers (though Graham prefers to describe himself as an essayist) who seem to have gradually transitioned towards writing about economics starting from their more specialized subjects (cryptography, mathematics and lisp respectively).
I guess this is because economics is a very powerful subject - if you want to change the world you have to make it worth peoples' while to do so, which means you have to set up the economic conditions for it to do so. Conversely, if you know (or think you know) how the world is likely to change in the next few years you can use economic principles to figure out what to place bets on (invest in).