Is there something about Dominion that naturally attracts programmers or are they just more likely to be active forum goers?
It's a combination of several biases in action. Computer programmers and other people with similar occupation/training/interest are probably more likely to play board games in general, and they are certainly more likely to use online forums. Also, Dominion probably attracts that bunch a bit more than some other games, but I would not except that difference to be that big. However, competitive dominion and in particular discussing card combinations etc. again should imply a bias in favor of programming-minded people. Finally, you can often also spot a programmer based on how they write (about technical content at least), so there's a bit of an observational bias as well; you see a bunch of programmers but don't directly realize how many non-programmers there are.
I'm personally not really a programmer, but my PhD is in computer science, so not that far either.
Note that the above is all about correlations, not causation.