The short answer is that Pro Tools is capable of creating and deleting huge files on a system. If a user with no Administrator privileges isn't normally allowed to delete these files then Pro Tools shouldn't let them delete them either. If Pro Tools gave Administrator powers to non-administrators there would be a lot of potential problems.
Historically this has always been the case with Pro Tools, whether on Mac OS 9 and previous (where there was only one user who had the equivalent of Administrator access), or on Windows NT, 2000, or XP.