Glen Schofield, studio manager at Visceral Games has said that while Dead Space wasn't a runaway success at retail, the used video game market has seen the new IP's install base almost double.
"... we also did studies on sort of how many unique users there were on the PSN network and Xbox Live. And realized, you know what, there's over three million people that have played Dead Space," said Schofield on the second episode of EA's official podcast to talk games. "Maybe we've only sold 1.5 million or whatever the number is. But there's something there because that means that, OK, there were a lot of used sales. So there's a lot of people when I go out and talk to [them]... it seems that everybody has played it or heard about it or whatever."
With the huge popularity or the used video game market it seems you can no longer judge a game's success on its official sales at retail. Recently Microsoft Game Studios boss Phil Spencer revealed that the Crackdown fan base has been significantly extended through used game sales.