There are two FeatureReaderIterator classes:
both are identical in purpose and almost identical in code.
The first being the one DataFeatureCollection.closeIterator( Iterator<SimpleFeature> close ) does an instanceof check to call the iterator's close() method, but is not used as far as I can see by looking for references to it.
The second being the only one referenced, used by the arcsde and wfs modules. But close() being ignored since DataFeatureCollection does not check for it.
The solution would be to deprecate the one in the org.geotools.feature package and make it an empty class extending from the one in org.geotools.data.store for 2.5.x and just remove it on trunk.