I've noticed this before, but really noticed it this morning at L'Enfant: Metro appears to be removing a lot (but not all) of the old brown pylons (See L'Enfant, McPherson as examples - you can see where the pylon is by the ugly round circle of concrete). I guess the wayfinding/station name display benefits of the pylons have been surpassed by the new signage hung on walls or the ceiling. Removing the pylons opens space on the platforms, makes it easier to navigate in crowds, and opens lines of sight. One drawback that occurred to me is that the pylons have braille on them, whereas the wall mounted/ceiling hung signage does not.
Living in Broadlands, VA; Working at Half & L SE, DC.
