Microsoft has recently released a KnowledgeBase article KB2401954
which gives instructions on how to modify certain registry settings to force Windows 7 and Vista to power down USB devices after using the Safely Remove Hardware feature. You can make these changes either globally or on a per-device basis.
After making these changes, the power/activity light on USB drives will go out after safely removing the hardware. The behavior will now be the same as in Windows XP.