That just suggests that the powers/martial maneuvers would be well organized into trees not that access to them should be limited by class. I don't see why a ranger shouldn't have access to the same fundamental fighting styles as a fighter.
I'm not sure how it suggest that at all so you would have to break that down for me further. You seem to be saying a better map for Powers would be to the Feat System rather than the, historically, siloed Class Feature System. 4e certainly isn't predicated upon that idea. The Powers are effectively Features that express the focus of the class both mechanically and in the corresponding fiction. Further, it seems that you're suggesting that the class structure in 4e should be diluted by way of free access to all powers within the power source (or at least specifically the Martial power source). It was my understanding that lack of differentiation/homogenization of the classes was one of the primary sources of angst amongst the edition's detractors. My analog map would be as follows:
- In DnD we have Adventurer as the generic career header for PCs.
- The MMA analog would be Fighter.
- In DnD we have our Class structure that expresses PCs' ability/practical application of field of study within the fiction through siloed features, spells, powers.
- The MMA analog would be the Primary Fighting Discipline that expresses Fighters' ability/practical application of field of study within the ring through mastery, nearly to the exclusion of other disciplines, of their primary Martial Art.
Historically in DnD (outside of some UA stuff and Skills and Powers), Classes' primary disciplines (features, spells, powers) are exclusive to them and it is borderline heresy to expect otherwise (hence the backlash against Skills and Powers). Giving out Fighter Weapon Specialization, Theif % skills or Backstab/Sneak Attack, Ranger's Favored Enemy, etc to all martial classes would seem to be a revolutionary idea (and again, would not be without controversy...and I'm sure we've all seen people loose it at the mere thought experiment of such an idea). However, there are means to access them and round out your PC; Dual-Class, Multi-Class, Hybridizing (in the analog above, this would be an MMA fighter rounding out his game through the study of the fundamentals of a secondary discipline). This is one way in which the Ranger has access to the Fighter's Fighting Style. The other way is in class choice at character creation (expressed in the fiction as seeking out a master and training, joining a lodge, growing up in the wild, military background, etc, etc).