- It's not cheap it's basic security. Someone with a limited user access account shouldn't be able to affect system-wide changes - that's just common sense.
Hm... a program that was installed by the admin and that writes to its own folder (no other locations) is not having "system-wide" effects. Whether you can write to the mIRC folder or to the user data folder, you're still changing/writing the exact same file(s).
I can see making it so that programs cannot write to OTHER folders besides user folders or the install folder. That prevents those "system-wide" changes and prevents a program from affecting other programs and so on. I see no need to prevent changes to a programs own files. If anything, prevent changes only to specific files (like EXE files) rather than INI files and TXT files and so on.