The debate existed under different names such as "N00bz vs 1337" "Casual vs Core" "Button Mashers vs Advanced" players. The ongoing dilemma between designing games for casual or core audiences with each side adamant games must be designed and developed for a particular group to be successful.. Trying to design for the casual market and you "dumb down" games too much and alienate the core market. Trying to design for the core audience and you alienate the larger casual market by devising mechanics too complex. Casuals may constitute the larger purchasing market, but it's through the reputation of a game from the hardcore that lays the reputation of a franchise and foundation contributes to profitable squeals. The bottom line is you want the game in as many consumer's hands as possible. So why not design and develop for both?

The 3rd pillar of the fundamental truths of game development is Games are for Players. The principle that developed from this understanding is:

1. Build for the masses design depth for the advanced

Depth should be done in such a way that it's not necessary, but is ideal for maximizing performance. Thus the masses don't have to, but can still "accidentally" access more functionality. Advanced players can apply their skills and purposely access deeper game play mechanics or tactics due to their higher level of understanding or superior hand dexterity. Gears of War and Bayonetta have game play mechanics that are devised for both the casual and core audience.

Gears of War 2: Reload Mechanic:

Each weapon can chamber "X" amounts of ammunition. Once the chamber is empty the weapon needs to be reloaded before being able to fire. Reloading weapons was developed in two ways:

• Masses - Fire until ammo is drained from weapon. Automatic reloads. Don't need to worry reloading.

• Advanced - Manually reload with a risk reward system. Properly time a button press to stop the moving bar to land on the sweet spot and you reload faster and get a damage boost. Failing by pressing too early or too late and your gun jams and takes even longer to reload. 

Picture taken from Gears of War Gears 2 gamers blog

Bayonetta: Very Easy Automatic Mode

The reverse of the principle. The combat design is intended to be complex and difficult for the hardcore market. Platinum Games developed an automatic mode for the players that lacks the desire, skill or time to master the hardcore game play mechanics. The depth of controller interface and decision making is available for the Core player, yet it's not necessary for the casual player in order to advance through the game.

• Masses - In Hideki Kamiya, director of Bayonetta, words from his blog "This is the power of Automatic. Automatic can be used on Easy and Very Easy difficulties, and leaves the most complex controls up to the CPU." Play one-handed.
• Advance - In another blog Hideki Kamiya implies the intent for the hardcore audience with "For instance, with Bayonetta, we would hate for someone to think it is a heartwarming tale and then buy the game to discover it is really a sadistically hard game (I hope…) where you play as a witch who laughs as she destroys angelic enemies."

Most decisions will be made with the target audience in mind. Designing mechanics so that the game is enjoyable  to as many people as possible is common sense. Design the core mechanics so that the casual has accessibility  in game play but design depth that the hardcore can take advantage of and improve performance. Who cares how the player plays the game, as long as they had fun and bought it new ;)