Poser and Bryce didn't begin as sister apps, they wound up that way not long after version 2 of each, when Fractal Design and Metatools teamed up to become Metacreations. Metacreations were (allegedly) to make the two apps work closely together for versions 5, but they 'repositioned themselves in the market' instead. There has been not a glimmer of Curious Labs and Corel making similar efforts for the future. :-(