On Sat, 7 Feb 2009 15:49:01 -0800, cox wrote:

Whoever wrote
the date function did not know what is considered an elementary school
knowledge that a year that is multiple of 100 is leap year if and only if it
is a multiple of 400.

The story I heard:

When Excel was first released, Lotus 1-2-3 had the market almost to itself.
This bug (considering 1900 to be a leap year) was present in Lotus 1-2-3, and
the Excel developers were instructed to maintain it in order to provide
compatibility with their major competitor.

See also http://support.microsoft.com/kb/214326

--ron