Q: Why do I have a list of modern applications on my Windows 8.1 Start Screen with a download arrow on them?
A: Windows 8.1 adds the ability to synchronize the Start Screen content between computers for "Modern" applications. If you are on a machine that doesn't have the Modern application installed, the icon will still show with a download arrow, as the screen shot below shows. This makes it easy to then install the missing applications by just clicking the download icon.
To control the synchronization of the Start Screen, open the Settings charm and select Change PC Settings. Select SkyDrive, then Sync settings. Under Personalization settings is the option to synchronize Start screen.