One of the questions that has come up is why RFC 3339 style dates were chosen for the date format in Atom. The simple answer is that any date that is conformant to RFC 3339 is also conformant to XML Schema, ISO 8601, and W3C Datetimes.
The slightly longer answer is that all the other schemas are more complex than RFC 3339. In particular the daddy of them all, ISO 8601 is the most complex. For example, all of the following are valid ISO 8601 dates:
- 1997-07-16 19:20+01:00
Care to guess what that last one represents?