Indeed. And one obviously has the choice of whether to run ground wires out to both jacks or not depending on the type of jack sockets used. Some people may use the plastic-bodied jack sockets, which are often used on pedals (especially with stereo or switched outputs where the increased switching functionality offered by them is utilised). In this instance, you'd certainly need to run ground wires to both jacks.

But I've had bought pedals where a ground lead was used to only one jack, the connection jacks became loose and/or the paint hadn't been cleared off the jack areas, and so performance became intermittent. I've sometimes run a ground wire myself between the two sockets to cure that.