Almost all of the campsites at St. Marys are pull-throughs. Depending on which site you are looking at, part of the Driveway Length may also be shared with adjacent campsites. Some of the pull throughs also have pretty tight turns, limiting maneuverability of your combination.
I have also found that vehicle length means different things at various NFS and NPS CGs. For some, it's the total of your TV and trailer. For other CGs, it's only the trailer length.
Also note that the example you posted also shows a moderate grade. They may be trying to account for how far up or down your tongue has to be to get level.
