XBox360 games that feature cooperative gameplay

This is the query: 
 
http://api.giantbomb.com/games/?api_key=XXXX&concepts=108&platforms=20     
  
The results are the same than this: 
 
http://api.giantbomb.com/games/?api_key=XXXX&platforms=20        
 
I think there are games in XBox360 that don't have co-op modes. Am I doing something wrong? 
 
PD: thank you

You're attempting to filter the results. You can't actually do that, so it's acting as if you didn't.