Maybe due to missing high res sat pics for OSM use ?
Landsat and bing offer only low res pics. So it's hard to map much more than corse information. Unfortunatedly we are not allowed to use Google sat pics.
But compared with other maps, there are more details in OSM.

Have a look at http://wiki.openstreetmap.org/wiki/WikiProject_Germany/Luftbilder
You will find some sources for high res pictures from that area taken by user http://wiki.openstreetmap.org/w/index.php?title=Vertical_Aerial_Photographs/User:MartinDornfelder&action=edit&redlink=1
Maybe there is some helpfull input for your upoming work.

The actual landsat pics for that area are much too poor to be used for detailled mapping.