Most people wouldn't believe that today different software gets different date/time results.  

Because:

The industry does not have date/time standards for maximum range and minimum precision.

The industry does not have standards for maximum duration calculations or rules to minimize errors because date/time does not have associative properties.  The ISO-8601 duration can minimize the errors.

If ISO-8601 standardized the maximum date range and a minimum time precisions:

It would eliminate Internet, SOA and Web-services date/time interoperation incompatibility.

It would eliminate different systems getting different results for the same date/time problem.