You are bringing in individual layers rather than the whole map service. Individual layers get rendered on the client as "feature layers". They do no support labeling. When adding services to your map you must use the root map service layer in order to have labels.
Review the documentation on the different layer types- http://help.arcgis.com/en/webapps/silverlightviewer/help/index.html#//017700000025000000
You are bringing in individual layers rather than the whole map service. Individual layers get rendered on the client as "feature layers". They do no support labeling. When adding services to your map you must use the root map service layer in order to have labels.
Review the documentation on the different layer types- http://help.arcgis.com/en/webapps/silverlightviewer/help/index.html#//017700000025000000
With all respect, this seems to me rather poor architecture or design (feature layers don't support labeling) that using labels requires multiple map services just for a single web application.
Let's say we have countries, regions and subregions that should be displayed or not. I would then need 3 additional map services to enable labels for those 3 polygon layers? Which would make a total of 4?
Makes me expect the number of map services needed explode exponentially.
Or did I get something wrong?