I think this really, really nails it on the head. This conversation about rangers reminds me so much of the psionic conversations. It follows pretty much the same lines.
There are a group of gamers that are really passionate about psionics and nothing less than a complete psionic subsystem separate from the magic system will do. Then you have a larger group that probably doesn't really have any strong opinion in either direction. Then you have someone like me who isn't all that enthusiastic about psionics in the first place and is really against the idea of adding an entire subsystem like 2e or 3e psionics just so that one player can play a psionicist.
Complexity increases exponentially. Every subsystem needs to work with every other subsystem and the more subsystems you add, the more complex the game gets. And, it often falls to the DM to police these sorts of things since I cannot possibly be the only DM out there who has players who are ... not particularly thorough in their understanding of the rules that apply to their character.
Which just adds to the workload of the DM.
D&DOne has the stated goal of streamlining and making things easier to run. They've been pretty clear about that. They are going to make the game easier to use at the table at the expense of complexity. We see this in the monster stat blocks and in how the classes are now shaping up. Which means that any calls to increase complexity are just not going to get any real traction. People don't want a
more complicated game. Running D&D is hard enough as it is. Adding in a subsystem for rangers, which may or may not come up in your next campaign, or even the one after that, but will come up two or three years after the release of D&DOne - meaning that the DM now has to go back and relearn that stuff just so Dave can play that ranger.
From a strictly practical standpoint, you cannot really have separate subsystems for half the classes while the other half the classes use the standard systems. Not when you have so many classes. It makes running the game so much more difficult - you run one campaign where everyone is a standard system - fighter, rogue, wizard, cleric and then the next campaign you have ranger, monk, psionicist, artificer and the poor DM's brains leak out their ears.