EA Games marketing boss Laura Miele, in a quote with CVG UK, has revealed that concern of the frightening single-player of Dead Space 1 and 2 contributed to the creation of co-operative play for Dead Space 3:
We were hearing feedback that they love the thriller game, but it was pretty scary, and the obvious next step was that they wanted to play with someone. So we introduced co-op into the game.
Luckily, this won't mean that Dead Space 3 will be less scary, or at least that what's being suggested:
The horror of Dead Space is still all there. It's still true to its roots and no less scary, but people felt far more comfortable playing it with someone else than they did doing it on their own.Personally, I would rather go to scary movie with my husband rather than sit at home with the lights out watching one on my own. We're looking for that to reach out to consumers that perhaps were not open to Dead Space 1 and 2.
[Source]