With spells like "Commune" and "Contact Other Plane" in D&D, it's kind of hard to not have gods. Actually, thinking about it, the type of magic you have available really has an impact. If you have level 20 wizards, there's a pretty good case for saying "Gods exist" because a level 20 wizard can create a plane of existence, summon life into it, etc... And if gods don't exist, then there's a power vacuum that will be filled.

Now, a relatively low magic world has the potential not to have anything that could fill the role of a god.