A sociological phase transition in the D&D genre

In the good old days, the roleplaying experience of Dungeons and Dragons was designed to be a reasonable approximation to the late Middle Ages. In particular, everyone's character had a formal class that he or she would belong to. There were fighters and clerics, paladins and rangers (presumably "special forces" rangers, but with the combat skills of park rangers), wizards and rogues. This was the medieval mindset: everyone had a pre-defined rank and role and life, and yet the adventerous player character could test his luck with the wheel of fortune.

Now the old roleplaying system of "formal" classes has broken down:

While I applaud the intent of 4E [Dungeon and Dragons Fourth Edition] to give every 1st level character a fighting chance via a ton of hit points (and healing surges) I think they just went too far with the various powers.

By giving Powers to all they've stripped away the relevance of those powers. Once every one has them, they cease to be anything special. Where's the noticable difference? Where's the defining characteristic of the character?

The answer is that it depends on the character's role. The Controller directs traffic. The Striker deals out damage. The Defender holds the line. The Leader gives out the buffs. Every class has a set of powers that support the given role. That's what defines the 4E character. The role within the party has become king.

Dungeons and Dragons now seems to be exclusively focused on performance in battle as the key determinant of the quality of the roleplaying experience (where's Dr. Freud when you need him). The pressure to fight effectively has correspondingly become so intense that the old "formal" character classes have disintegrated under the pressure of the new "empirical" character classes.