But in all of mathdom, 0777 = 777. I can see reasons to break convention. The consistency is nice; everything without a prefix is decimal. Easy to avoid hard-to-spot errors.

I deal with decimal data on a daily basis that has leading zeroes (input from non-Perl sources). I have more use for fixed-width columns of decimal numbers padded with zeroes so things line up (for example) than for octal numbers.