This is where Windows gets messy on what the idea of an admin is. It came from a history of 'full admin by default' instead of a "you never use root unless ___".

If your grandma had a Windows XP box with a default user, it was a 'full admin', but most likely grandma had no idea of how to administer it. So you ended up with a SYSTEM privilege that is even above admin. The full admin needs to promote themselves (run as) temporarily to that priv to change some things.