Back with 1.0 there actually was a free component released that included WP in Joomla. The problem is it was never maintained past the first release so it became insecure pretty quickly.

1.5 was really just a code upgrade from 1.0, for the most part. Usability/functionality really didn't change that much. There is no doubt it's always been an awful platform for blogging, so it's nice to see something coming back, even if it is commercial.