I... Wouldn't say that. I actually got a hentai game on Steam to see if it was censored or not... Nope... Dicks, breasts and pussy "cats" as far as the eye could see. And this game was near the top of the store. So I wouldn't say they would always be censored.
Hmm... If I remember correctly, Nekopara got some free DLC to uncensor their game. And that's a pretty well known series. And I don't think I need to mention what it uncensors, haha.
Steam only recently allowed full-on hentai on the store, so not everything is. Newly released stuff and updated stuff probably is though, since it's allowed now.