@ZeLonewolf, My understanding is that driveways must have specified access tags for them to be considered routable by certain software using OSM data. It also is not incorrect, as one certainly could access a driveway by horse to reach a destination.

@Mateusz Konieczny, sources for my edits are any one or combination of the following: GIS data from the State of Oregon, GIS data from Lincoln and Lane counties, GPS tracks that I have collected, decades of imagery (including LIDAR) from various sources, street level imagery from Google and Bing, surveys, and easement agreements.