As a HUGE fan of Pixar I thought to myself; what makes Pixar films successful? Any film critic will tell you it's the fact that the films are written for everyone and not just young kids. They focus on concepts that everyone can relate to regardless of age, sex and status. Finding Nemo was all about the bond between a parent and a child. Toy Story was all about mentors competing for the attention of their protegee. Wall-E was all about a dude trying to get laid.
What makes Nintendo games successful? Well games in the Mario franchise for one have always had a long lasting appeal with a consistently high standard of innovation balanced with familiarity. They have also been relatively accessible compared to a lot of contemporary successful franchises. A grandfather can sit down and play Super Mario Galaxy. Try and get him playing Modern Warfare 2 and it will probably not go as smoothly. Anyone can sit down and pick up a Mario game. Anyone can boot up and play Wii Sports without out any prior skill or knowledge.
Now I think that a lot of people confuse accessibility with wide appeal. Video games in general are fun. I mean that's why they are a billion dollar industry, and why COD:MW2 grossed more money than Avatar. People like playing video games, whether they are "hardcore" gamers or too cool for school "casual" gamers. With that said, games like Wii Sports, or Mario Kart feel more like board games to me. It is a similar experience to playing Monopoly. It is a relatively low skill, very social experience. There is no real, life changing, deep message being sent to Nintendo players. Watch a movie like Up (which I watched with my 8 year old brother and enjoyed a similar moving experience) and it affects you emotionally, again regardless of age, sex or status. Most Nintendo games aren't emotional experiences like that. You won't learn to love again playing Wii Music. You won't feel the bond of an emotionally distraught father trying to reunite with his son.
To sum up my point, Nintendo makes video games that are dumbed down for the masses where Pixar makes art so brilliant that you can not help but be moved. Take that Miyamoto!