I have pages and pages of discussion, in Dragon Magazines and White Dwarf magazines from the 70s and early 80s, of effective ways to play certain classes, of feasible builds for certain classes, of common mistakes that new players might want to avoid, etc. This sort of play advice has always been part of the game. The rulebooks, at least since Moldvay Basic and AD&D, have always included some of this sort of advice (eg advising players of MUs to keep their PCs out of melee). The label of "roles" is an aspect of such advice - it is advising actual and prospective players on what sorts of combat actions their PC is likely to be good at, given certain build choices (and 4e makes choice of class the pre-eminent build choice - in this respect it is more like AD&D or Basic than 5e, which makes sub-class and background and even race as or more significant than class).
4e does not focus exclusively on fighting.
What @
Hussar (correctly) stated is that 4e's role labels are solely about fighting.
If the game is written in stone tablets that have been handed down, then this sort of answer makes sense. But the game isn't fixed in this way.
For instance, Phantom Steed began its life as an illusionist spell, published in Unearthed Arcana and before that, I believe, in Dragon 66. And it summoned one steed. What makes it appropriate to give that spell to wizards rather than a distinct illusionist class? And to make it useable as a ritual to summon multiple steeds (a 4e innovation)? Why not make the ability to call mounts part of the ranger or druid's class abilities (to call a herd of friendly horses, camels or whatever)? Or a background feature for guides or nomads?
From the point of view of designing the game, making these calls is deciding that some character builds - whether defined at the level of class, sub-class, background, race or feat - will be able to perform a particular function that the game might call for, while others will not.
From the point of view of playing the game, it is helpful to know that (for instance) the same characters who are good at healing are also good at dealing with undead (true in 3E, mostly true in AD&D, frequently not the case in 4e or 5e); or (for instance) that it is thieves and not fighters who are better at skirmishing and stabbing from the back (true for backstabbing but not skirmishing in B/X and AD&D; true for both in 4e; true for skirmishing but not necessarily backstabbing in 5e); etc.
None of this is self-evident simply by describing a character as a cleric, a fighter, a wizard or a thief.
Not if things are required of them that they can't do. A wizard can't have healing spells in his/her spellbook, for instance. Why not? Because decisions have been made, by the game designers, that different sorts of characters will have different sorts of functions that they perform. If you want your party to be able to heal, you need to bring along a character other than a wizard.
Thinking about what the capabilities of a given PC are, given how their mechanical abilities interact with the typical sorts of situations the game throws up, has been part and parcel of the game for a long time now.