The LED is working as designed, but it's an area where MOT has changed the behavior from D1 and D2... I suspected tidbits was asking about that LED but I wanted to make sure before responding.
We've changed the UI paradigm for the white LED located next to the microUSB port since evolving from D1/D2 to D3, and the reason you don't see it lighting up nearly as often is that the LED under discussion is no longer "sign of charge", it's "sign of life".
There are two physical LED's on the phone (not counting the caps-lock and alt-lock LED's on the QWERTY), plus the display / software UI of the phone itself -- all 3 are viable means to convey information to the user. After benchmarking the competition and internally reviewing proposals for streamlining of our UI notification flow and avoid putting multiple behaviors (such as notifications + sign of charge) on the same LED, D3 does the following:
1) Medium used to display notifications: green LED above display (also flashes red when battery is low)
2) Medium used to display sign of charge (what you guys call "charger indicator"): display / software UI
3) Medium used to display sign of life: white LED next to microUSB
Sign of life is something used in very rare circumstances, such as a bone-dead battery, where you do not yet have enough power to light up the display (to show sign of charge through the phone UI) but we want to reassure the user that yes, the phone is alive and charging up. Once the phone gets enough charge to activate the display, you'll see the sign of life LED wink out.
Warren @ Moto