That is why I suggest installing it on a new partition or drive.
The issue I have, is that WinXP enjoys ~85% marketshare of all installed PCs. Why would you make a new OS, that will very likely result in users losing data? This is a customer relations nightmare. “Here, buy my new $300 OS, that does nothing really substancially more or better than your current OS - and I will wipe all of your data, your tax records, your digital pictures and other ‘priceless’ data from your PC for you”.
Previous versions of Windows let me upgrade my OS, and they also changed FAT32 to NTFS without destroying my data. So, why do I lose any data that I fail to backup, if I upgrade from WinXP? I can upgrade WinXP to Vista, and you can upgrade Vista to Win7 without losing data. Why can’t I upgrade WinXP to Win7?!?