Our game Defender's Quest will be five years old in just a few days, which is a good opportunity for a retrospective on how Steam has changed in that time.
[quote]So how can you replicate our success? I’ve absolutely no idea. All I
can do is list some things we did that I think were important and seemed
to work for us, and try to back that up with whatever data I have
available.[/quote]
I have two ideas.
You chase absolutely every marketing opportunity you can, while trying to be among the first to do so. When Cards first released, there were precious few games with cards on Steam - mainly expensive major releases. DQ was a cheaper game, you churned it’s cards out quick and many people bought it just to try and get their hands on some cards. You’re doing the same thing with the Steam Controller, being one of the few vocal devs working with it.
You being a vocal dev. Being friendly and involved with the general gaming community with all your many articles, as well as your customers, built you the reputation as a Pretty Cool Guy. Fairly often people recommend DQ while simultaneously mentioning how the developers are cool guys who have maintained the game for a long time and take care to fix any bugs that pop up, no matter how small. Most developers don’t really do too much customer interaction, they seem to release their game and move on.
Be among the first to jump on a new thing + don’t be a jerk = Recipe for success.
Just a note for future analyses- New Zealand is actually a primarily English-speaking country, too. 
After all the years I’ve been reading and enjoying your articles, I made an account to say just one thing: I started reading this one about 5 hours ago. I just now read the last few paragraphs. The links and references you include tend to be so very interesting, that they consistently make me fall down very deep internet holes, out of which I consistently emerge smarter. Thank you for taking the time to do that.
And btw, all the other analysis aside, the reason for your success is the fact that DQ delivers supremely enjoyable gameplay before everything else, as pretty much everyone who’s ever played it agrees… I know that doesn’t help write useful articles, but really, it explains a lot.