Warrior: melee damage > melee control > maneuverability > party buffs > survivability > ranged physical damage
BML: party protection > survivability > healing > melee damage > ranged magic damage > melee control
Now, each individual player would be able to modify this scale with weapon choice, utilities, traits etc., to the point where any one of those roles could be their area of expertise, but the chart shows where your class is the most versatile. You might be able to build 9 different viable variations on a melee damage warrior, but there's only 1 viable way to play a ranged damage warrior; or there are a lot of ways to play a prot BML, but if you want to play a melee control BML your options are narrowed down significantly.
That's kind of how I see GW2's system playing out. So to say BML is a defensive/support focused character doesn't mean that's the only thing it's capable of, it means that the player who knows they want to play a defensive/support role will find the most flexibility and freedom determining the specifics of how they carry out that role if they pick a BML. On the other hand, the player who picks a BML because they like the way it looks, or they just want to be a holy warrior or whatever, will still have the option to play whatever role he wants without feeling gimped.
If classes don't have any strengths or weaknesses, or specialties of any kind, then it kind of defeats the point of a class system as far as i'm concerned.