why can I access My Documents in Win7 from XP (Win7/XP dual boot)?

I was running a dual boot XP SP3/XP SP3 until I recently clean installed Win7 32bit on C: partition (while keeping the other XP install). I used a boot manager to "find" my XP install, and I now dual boot Win7/XP. Both OSes start and run like they are supposed to.

My issue is with Windows 7 MyDocuments security. Quite by accident, I discovered that when running XP, I could access, rename, change, and delete files in my Windows 7 MyDocuments folder. I went to Win7/Windows/system32 to see if I could rename or delete system files (yes, I made a backup just in case) but was denied. I booted into Win7 and tried the same thing to XP, but got the familiar "permission denied" popup.

Needless to say this was puzzling and very concerning as well. Why does Windows7 not give me a "permission denied" trying to access Win7/MyDocuments while in XP?

logicearth said:

Because you are a user part of the Administrators group on Windows XP. Those part of the Administrators group have access to your user directory, its part of the permissions, in the Security tab.

Was this something that was changed in Win7? Because when dual booting XP/XP, neither install could access the other's user files like MyDocs, and I always logged into each XP OS with my admin account. It seems this is a step backwards as far as security is concerned. Why would Win7 allow an admin to access personal files of another admin?