Which proves my point. Nintendos alternative games are mostly made on the outside. Sony makes everything on the inside but also uses outside talent much like Nintendo. The reasons are different though. These days Sony pumps out IP's at a greater rate than Microsoft and Nintendo.
I doubt Sony has released more first party games for PS3 + PSp than Nintendo has for Wii + DS.
And with the way things have been going for 3DS and the 1st party support I expect for Wii U in the future, I don't think that's going to change.