Linus is right because these are actually well known and easy to parse.

However, if instead of S_IRUSR|S_IWUSR (which I'd have to lookup up to parse correctly), it were possible to write "a-rwx"|"u+rw", it would be even easier to parse, without the need to memorize common octal numbers. In C, this could be achieved with the preprocessor, I believe, if you create a sufficiently smart CPP macro, especially since Linux is no stranger to heavy preprocessor use.