The exchange is profoundly unsatisfying because the question and answer don't really respond to each other. What is a fighter? In 3.x, it was someone who focused their talents on combat and weapon use. In 4e, a description of a fighter will always include the phrase "martial defender." A 4e fighter isn't just someone who focuses on combat, but it is someone who focuses on melee combat and occupying foes. From the hints we've seen of the Martial Power book, there will be a ton of fighter options covering a wide number of variants within that general role.
...but it is fairly clear that a class can be more than just a power source and role combination. Rogues and Rangers are both martial strikers. We can easily imagine an arcane striker who isn't a Warlock (a Warmage, say) or an arcane controller who isn't a Wizard. The difference? Flavor, I guess. Could the rouge and ranger have been combined into a single class with alternate builds? They probably could have been, but I guess the feeling was that the flavors of the two were distinct enough to justify separating them.
The thing is, Fighters don't really have that flavor thing going for them. I don't think the fighter class is much more than the Martial+Defender combination. I get the impression that any martial defender is going to be presented as a new Fighter build. This seems... inconsistent. Maybe it is simply that the fighter is the class that is most basic, lacking particular flavor? I think that represents a lack of imagination. We could have easily seen the fighter broken up into a few Martial Defender classes. Here are two:
- The Sentinel (heavily armored and often armed with a two-handed weapon) who focuses on guarding someone or something.
- The Swashbuckler (lightly armored) who focuses on high mobility, forcing everyone in an area to pay attention to him or else. (It has been suggested that Rogues make good swashbuckling types - but what if I want a swashbuckler who doesn't focus on massive damage, but rather focuses on getting in people's way?)