Why/how does Ownership Not Work Properly?

i recently had a problem with ownership of a registry file called "msohelp" (i think i know how to fix it). and there might be more ownership issues that i don't know about yet...

but i was wondering how on earth this happened in the first place. is it caused by adding/deleting users or re-installing xp home too many times? because i've done both. it just seems strange to have the ownership of this one registry file for microsoft office help messed up...

also, i've noticed that there are about 6 SID's when i am taking ownership. is there a way to delete the old SID's? or should i not worry about it?

thanks in advance.