Edit: just saw that it only concerns the west of Belgium (East and West Flanders… where I live): only a very restricted number of articles appear. There should be many more. Rest of the world shows the many articles fine.
This is probably due to the way the coordinates are formatted in the wikipedia article. If you want it to be fixed fast, just go to the articles which are not shown on PE, and copy the source of the coordinates and post it here. The, geomagik can integrate it into the next data treatment.
Example ( I did not check if this articles are shown in PE or not)