In the next release of ArcGIS Open Data targeted for night of July 16th, Administrators will be given an option to enable local projections used for Shapefiles. Sites with this capability turned on, will provide their Shapefile downloads in the same projection it was published in. This helps Organizations that are providing data to other GIS users who have a better understanding of working with projections.
To maintain consistency after the release all current sites will have the local projection option enabled, since projected Shapefile downloads are the current default. Administrators can disable this on a site by site basis, to provide their Shapefile downloads in WGS84. All new sites will have this capability turned off by default, and it must be a conscience decision by the Administrator to provide Shapefile downloads in the local projection.
All Shapefiles downloaded from opendata.arcgis.com will be in WGS84, providing a consistent projection across all datasets for citizens who are trying to make maps with data from different sources.