I can't imagine that the product hasn't made enough money that it wouldn't be viable to hire a developer, or to take on investment to expand the operation. ST seems to be the most popular code text editor amongst developers.
I bought ST just like many friends did. Sublime may be selling about as much as RubyMotion, which invested the proceeds in hiring very few, high-level coders that seem to be fully inline with the founder/original author.
Second, ST is not based on a freemium model. Only the betas are free (and that only as long as there's no stable release), for the stable versions you have to pay.
Second, the fact that since ST2 he was able to hire a second person to help him with the business side.