Here is the difference in a very simple example... can I play a Ranger who fights with his powers unarmed?
There are (at least) two ways of interpreting that question, I think.
Can you build a 4e PC whose class is ranger, and who is a mechanically viable unarmed combatant? Not from the books that I'm familiar with (though there may be stuff in Dragon I don't know), although I personally don't think it would break the game if the GM let you swap your martial weapon proficiency for the Monk Unarmed Strike feature - and now you could be a two-weapon ranger who uses fists instead of longswords.
Alternatively, you could take Monk Unarmed Strike as a custom feat - it doesn't strike me as any more powerful, feat-wise, than a Superior Weapon Proficiency.
But a second interpretation of the question is - can you build a mechanically viable unarmed combatant who is a wilderness guide and tracker? And I think the answer to that question is "yes" - build a monk, or a brawler fighter, and take feats, background options, theme and/or multi-class options that get you Perception and Nature proficiency. Or even go for a hybrid brawler/ranger or monk/ranger.
I think that any of these PCs will be as viable, in the 4e play space, as a 3E PHB ranger using Improved Unarmed Strike would be in the 3E play space. Perhaps moreso, because I don't know of any way for that 3E ranger to get his/her unarmed strike up to the same power level as a longsword.
So I think the answer to your question is "Yes".
Hey pemerton, upon further reflection I decided I actually want to go more in depth with my answer to you...
IMO the difference is that of customization. In your first example I get an archetype and the details of both concept and gameplay are left up to me to decide upon. In the second example I have to hope that the individual details of a simgle package will line up with what I want in both concept and gameplay.
OK. There's little doubt that compared to 3E, 4e emphasises "single packages" more, and customisation takes the form of choosing from long lists of big packages, where the fiddly stuff (powers, feats etc) tends to happen within constraints already set by those big packages.
But I don't particularly see this as a "role" thing. Rolemaster, compared to classic D&D and 3E, has a similar approach to spells - a spell-user has to choose a class, which determines a bundle of spell lists that are learnable, and there is no way of mixing and matching different spells onto those lists. But in Rolemaster this is not in service of "role" in the 4e sense. It is in service of flavour, and also (at least arguably) balance - no single PC can get access to all the best spells. Rolemaster does not have D&D-style "generic" wizards.
I see the class power lists in 4e as doing something similar - they ensure a coherent flavour, and serve the interests of balance. The connection of powers to role is reasonably loose, at least in my view. Fighters, for example, have a good range of self-healing powers, and also condition alleviation, which means that they tend to act as their own leaders (and given that they take a lot of the damage, obviate the need for more specialised leadership on the part of another PC). Fighters and sorcerers are also quite controller-y in certain respects, getting good forced movement effects. And I know from experience that a drow sorcerer using cloud of darkness plus force movement effects can play much the same role as a defender - locking down the front line without dying.
From my point of view, the objection to 4e's approach to classes isn't "roles". It's class bloat. WotC's sub-class solution is an interesting compromise (although capable of producing clunkers like the Binder) on this front, because it both reduces bloat and opens up more role flexibility. The conern for me is that it runs the risk of making certain classes "universal" classes - able to do everything - which then runs the risk of killing off other, more flavourful, options. The witch being a wizard rather than a warlock I think is a possible example of this, although I'm yet to learn more about the class than what the WotC previews have shown.
A Power Source in 4E provides a way to overcome combat challenges. If you want a non-combat answer to problems, skills and rituals are the only thing available and they are provided to all classes.
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Prior to 4E, a class provided a set of tools for problem solving, both in and out of combat. Classes used to have a wide variety of answers available to them.
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Now, every class gets the exact same piece of the combat pie. To make sure everything is balanced, no one gets out of combat abilities beyond skills.
I find that the class skill lists, combined with player choices in respect of skill selection, tend to support out-of-combat roles in 4e also. And because rituals are linked to either class or particular skills, which themselves have overtones of spell use and mystical education (Arcana and Religion), I find that rituals also tend to travel with particular power sources and flavours of PC.
I also think that it's just not true that no one gets out of combat abilities beyond skills. Some PCs get rituals, which are not skills, and which are out of combat abilities. And some PCs get utility powers which are not combat abilities. For example, of the 21 wizard utility powers in the PHB, at least 9 have obvious or primary non-combat utility, and of the 18 warlock utilities, at least 11 have obvious or primary non-combat utility.
And there are also feats that confer non-combat abilities. The wizard PC in my game, for example, has two of them: Skill Training (Dungeoneering) and Deep Sage. The sorcerer PC in my game has the Arcane Familiar feat - which, even more than rituals, is something that tracks power source - in order to get an air mephit, in part for the bonus to Bluff (which he uses to hide in combat) but also so that he can read and speak Primordial, and have an invisible flying scout.
It may be that some players choose not to select powers or feats that enhance their out-of-combat capabilities. But I don't think it's fair to say that the game doesn't provide them.
Why can't any class support being a "first rate striker" (or whatever)?
If it does this by having a menu of class features, chosen as part of the build process, then we're back in sub-class territory.
If it does this by having certain powers that are inherently stiker-y (like the Barbarian powers with bonus dice) then we're either just in a different sub-class territory (with power selection rather than feature selection being the focus of build choices), or we're in potentially overpowered territory - if I get to combine my striker-y power with my defender-y class feature, for example. No doubt this issue of balance can be handled with care - someone upthread already mentioned the STR paladin 4W powers, for example. But the greater the care, probably the less the striker feel.
If it is done not as part of build but as part of play - changing stances, for example, from defensive to agressive - then I'm sure it's viable. (Burning Wheel has a stance mechanic, for example, allowing the use of an action to shift between defensive, neutral and agressive stances - with the non-neutral stances giving bonuses and penalties to the appropriate sorts of actions.) I'm personally not sure it's better. Nor worse. It would be different from what I'm used to in D&D, or expect from a class-based system, but that's not necessarily an objection.