Now FWIW; 4e has allowed us to break the secondary roles being niche-protected. Rogues aren't the only trapfinders, clerics the only who could cast raise dead. In fact, only COMBAT roles (striker, defender, etc) are hard-wired; a party with a paladin, bard, ranger, and druid with proper skills (perception, thievery) and feats (ritual caster) can do every major thing a fighter, cleric, rogue and wizard can. (Can't say THAT about 3.5!)
Though I think here might also lie a weakness. 4E does not spell out the non-combat roles. I am not saying it has to lock a class into a non-combat role, but to make it explicit somehow that these roles exist and how they effect non-combat situations like dungeon exploration, social situations, wilderness travel, investigations, research (or plain knowledge)
A Wizard is a controller in battle, but outside he's typically a sage.
A Warlord is a leader in battle, but he might be a sage or the groups face outside.
A Ranger is a Striker in battle, but he's typically a guide or explorer outside of it.
A Rogue might be a Striker in battle, but he's typically a dungeon explorer/trap-guy in outside of combat.
Well, in my theoretical "class-less" but "role-focused" version of d20 Modern, this is exactly what I would want to do. Allowing people to mix their combat role with their non-combat role and make these explicit.
Even if you make the non-combat roles more explicit, this doesn't have to mean going outside the role is impossible or a bad idea (in fact, that is already true in case of combat roles, the most obvious example people multi-classing into classes with different roles). In 4E, it would be as easy as taking Skill Training (the very mechanic that already serves us to avoid the "secondary role" niche of classes.).
I think one interesting aspect of this is that I believe that many "old school" people that don't like the combat roles might like the idea of the non-combat roles more. Because these roles are mapped to typical dungeon exploration roles, and from what I gather, this is what people associate the most with "old school".
For the storytelling fraction, these non-combat roles would also be helpful, because they explain the focus of your character and allows to decide which character is critical in which aspect of the story.