Because of the size of the Ultra Sculptor, both the handle and the brush- head would have to be re-tooled and the expense would be prohibitive just for the one brush. Although a favorite of mine too, the U.Sculptor is not the number one selling brush in the Creative line.
You'll love it Fi! I've got two, both with Pro Styler heads. I switched from the Ultra Sculptor to use it. They are great. I was clearing out my drawer and came across my old U S and had a little play with it. Ah!.....such memories
The diff between Crystal Touch and Master series is in the style.
There are a few different sizes out there:
The Crystal Touch brushes have a clear acrylic handle, where the Master Series have chemically resistant anodized coatings and replaceable heads (very cool).
The Master Series brushes all have the same handle, but CND only makes the Sculptor and Pro styler heads for the line.
The reason is because the Pro Styler and Sculptor handles are the same size... so they are interchangeable.