It's easy to answer the OP question:
A) Theres nothing wrong with their 1st/3rd party ratio.
B) It wasn't a problem last generation, considering raw units sold.
C + D) A title which stands out and actually gets 'market development' funds will find a place on the shelves. Infact it will push other titles aside. If a game doesn't have any funding on marketing its a crapshoot as to whether or not the retailers believe its going to sell so unit numbers are lower. If a game gets multiple shelf spaces at retail then it sends a message to the games buyer that it might be a title to at least consider. To be successful you also have to look successful in the business, and simply having a lot of boxes on the shelf can do that. Nintendo gets that treatment automatically because they have a good reputation, the third parties need to establish that same reputation. They can only pull the same tricks for so long before the public and the retailers wise up.
Reputation is one of the things in the business that the publishers are too quick to throw away. Theres no other publisher in the industry that gives an assurance that if you buy one of their products you're probably going to like it to some degree. The same goes for other entertainment industries like Movies where both actors and studios are all keenly aware that releasing a poor product will cost them more than sales at the box office. The greater the potential investment of time/money the more having a great reputation is beneficial.