I see it in the manner that a movie theater would. Steam promotes and sells games, they are a distributor and they want to make sure what they distribute doesn't paint them in a bad light.
Now, a theater has films involving sex and violence, AS DOES STEAM. However, most theaters do not promote and distribute raw pornography. If they do, they specialize in it. I can see the folks running steam treating there service as such, seeing a game that is designed to be pornographic, and make the decision not to show it. It's not a shut down of creative express, or a reflection of the "Prudish American Standard" it's a company deciding the kind of content it wants to distribute.
Now, a theater has films involving sex and violence, AS DOES STEAM. However, most theaters do not promote and distribute raw pornography. If they do, they specialize in it. I can see the folks running steam treating there service as such, seeing a game that is designed to be pornographic, and make the decision not to show it. It's not a shut down of creative express, or a reflection of the "Prudish American Standard" it's a company deciding the kind of content it wants to distribute.