It's not a
slight advantage if you've ever had to parse through logfiles by hand or debug APIs with curl--it's a great deal more than that.
Why not, let's have some more examples:
In PHP (with a bug, because PHP is stupid and doesn't handle decimal fractions):
$dateTime = DateTime::createFromFormat( DateTime::ISO8601, '2009-04-16T12:07:23Z');
In C#:
DateTime time = DateTime.Parse("2010-08-20T15:00:00Z", null, DateTimeStyles.RoundtripKind);
In Python (stupid that it isn't in the standard library, see
https://wiki.python.org/moin/WorkingWithTime):
import dateutil.parser
dateutil.parser.parse('2008-08-09T18:39:22Z')
In Perl:
my $dt = DateTime::Format::ISO8601->parse_datetime( "2008-08-09T18:39:22Z" );
~
Interchange formats, say JSON blobs over a wire, should very clearly express what's in them, perhaps by using a very well-known standard which is human-readable, whenever possible. The fact that some languages haven't yet realized that this is an important-enough feature to put in their standard libraries compared with whatever esoteric academic shit they think is necessary (C++1x, for example!) is not the format's problem.
Hint: if you're consuming a web API, you are probably using one of the languages I gave examples for, or a very close relative. Just because your Haskell-on-M68k package doesn't know how to 8601 doesn't mean that using a nondescript number is a good idea.
Why, in the year of our Lord 2014, is this even a fucking question?
EDIT:
I'm sorry to be so mean in my language about this, but I've had to fight a lot of raging stupid with regards to storing timestamp data. I do not wish to see anyone else suffer unduly.