I've observed a number of plug-ins other than my own that have implemented their own scrolling. Two major use-cases:
- Scrolling free-form text.
- Scrolling rows of controls. For this, the common technique is to implement a fixed size array of the controls and then provide "up" and "down" scroll buttons that repopulate the array of controls. A built-in scroll-bar control could make this easier to implement, provider a nicer graphical presentation, and provide consistency to users in how the scrolling works.