I dispute the idea of it being a "huge commercial machine" just because people are creating themes for it and charging money for them. It's a blogging platform that has support from an ecosystem that builds themes—which is arguably a requirement for any modern blogging platform that wants to draw in regular (read: non-tech-oriented) users.
The average user wants a nice-looking site without a lot of work. Ghost wants to market itself to regular users. It just seems like common sense that they'd get theme-makers on board—especially since it played such a huge role in the growth of Tumblr and WordPress, respectively.
It's pretty easy to ignore and gets people excited about the potential here, and considering that Ghost is so new, I don't think anyone is getting rich off of it right off the bat.
It's seriously harmless and arguably healthy that people are interested in spending time creating themes for such a young platform already.