Because the version of the module is solely independent of the version of Drupal. The version of the module indicates API and/or UI differences. If you have version 2.x of your module in version 5.x of Drupal and then change it to version 1.x for version 6.x of Drupal; one tends to view the 6.x-1.x as the same interface as 5.x-1.x.
But I'm wrong and will shut the hell up.
Actually, I agree with Earnie here ;)
(Only about module versions being independent of Drupal versions).
-- Morbus Iff ( if i could change the future, i'd change the past instead )
Also, we have to consider what end-users think about 5.x-2.x and 6.x-1.x. My interpretation as end-user would even be worse: There seem to be two versions of this module, version 1 for Drupal 5 and also D6. And for Drupal 5, there is also a new and probably better version 2 that has not been ported to D6 yet. This means, we should move this discussion over to the original issue: http://drupal.org/node/136078 Thanks, Daniel