The simplest answer is because the iPOD software detects that it is unsafe (read: data loss) for your iPOD, Computer or both if you were to disconnect the cable without ejecting the device first.Here's what to do:On the Mac-- Click on the Finder icon Pick the iPOD icon.Navigate to the File menu--select Eject iPOD On a Windows OpSys device-- On the Start menu, click Computer (e.g. Windows 7).Right-click on the drive/device letter or iPOD icon (read: the icon doesn't always appear)Select Eject.The ......