To be clear, I wasn't saying that was how it will work, only asking. A post by Mary Jo Foley seems to say the contrary:
"For those wondering exactly which apps will need to be reinstalled, it depends whether the tester is running Windows on ARM or x86. On Windows RT devices, it's the Windows Store/Metro-Style apps that will have to be reinstalled; for x86-based Windows 8 systems, testers will need to reinstall both their Windows Store/Metro-Style and Desktop apps.
Windows 8 users who do not install the preview build and opt instead to go straight from Windows 8/Windows RT to Windows 8.1 will not have to reinstall their apps. All settings, data and apps will carry over.
Which seems to say be prepared to reinstall all the Metro apps if you try the preview. But even if all the apps need to be reinstalled, it should be easier for Surface RT owners. All your regular setings and data will sync right over when you log on with your MS account. Since all RT apps come from the Windows Store and are tied to your MS account, after installing the Windows 8.1 preview (and later when going to the final version) it seems to me that you'll be able to log in with your MS account, open the Store and re-download all the missing apps at one time if you've kept note of the ones you like and want.
I recently sent my Surface in for repair. When it came back it was a blank slate, so to speak. But as soon as I signed in with my MS account most things immediately came back and all I had to do was re-download my apps. It was fast and a no brainer The only things I lost were the particular sites I wanted in my news aggregators and my high scores in Bejeweled.