What you perhaps do not realize is that in tabletops and whatever involves human interaction these things are mixed in a way that they can't be clearly defined as in a video game.
You are one of five solo dudes. Game mechanics take care that you are one fifth of a team so the game runs smoothly for everyone's fun.
I agree that this should be the design goal and I believe that team focused mechanics for the player will fail to provide this. This is what I am arguing about. I know it is not apparent at first glance but I believe it is the case.
I'm not sure I see the disconnect of what you're saying, and the way things have always been in D&D, or any RPG for that matter. Party members in D&D have always had distinct motivations and personalities, and had specific roles to fill. They work together as a team to overcome obstacles and enemies, but nothing prevents them from having their own agendas.
The cool thing about 4e is that each character now is a valued part of the team, rather than being relegated to a henchman when the casters get to high level. Clearer class distinctions let each class shine and be VERY good at what they do, but also be lacking in some areas. The wizard might be able to fry dozens of orcs at a time or change the way reality works for a short time with a ritual, but when he's got a chain devil breathing down his throat, he's screwed. Good thing the paladin is there to defend the wizard and use his holy abilities to deal radiant damage to the devil.
3e characters tended to become lone wolves, who could easily overcome any limitations of their class with multiclassing, feats, items, or buffs. To me, that was bad game design. I don't know how many times I saw characters copy abilities of each other, or the powers one character gained as they grew in power overshadowed others in the group in their specialty area! (Clerics with Divine Favor, GMW, Divine Power, Righteous Might, etc overshadowing fighters for example). That leads to competition within the group, and possibly hurt feelings- not something you want if you're trying to have fun with friends.
I've found that 4e actually encourages roleplaying more than previous versions of D&D, but for a subtle reason. Because tactics and teamwork are the focus of 4e rather than rules mastery, that the players tend to work better together as a team and come up with ideas as a group. That pulls people more into their roles as their characters and thinking as their characters, rather than distancing themselves from their roles and seeing their characters as simply numerical representations to milk every possible bonus out of their stats for optimal success. Its a subtle distinction to be sure, but its something I've noticed becoming more and more pronounced the more I've played and run 4e. 4e is less powergamer and optomizer friendly, but more party friendly, and to me that is a HUGE improvement. It doesn't preclude inviduals acting as distinct personalities, or having conflict among themselves- but it does make it harder to step on another party member's toes, which is good game design.