You have read correctly that the Scroll event is not implemented by design, and you have problably read most of the literature, along with the wiki article on differences between Windows Forms and Visual WebGui, so I'm not duplicating any of that here.
It may sound like an easy task just to expose and/or implement the Scroll event firing, but it is really not as simple as it may sound, as the infrastructure needed to support the firing of that event is not available or ready within the framework, so there a a very much more to it than just exposing one event. This would require a huge effort and overhaul of all controls of the framework and has been discussed multiple times before with the same conclution that currently we do not support it.
To explain, so you better understand what we would be up against, then there are two parts in implementing this. First is what you have already done, overriding those properties so that you can change them from the server side code, and then on the next control rendering, those scroll properties would be in effect and your control is correctly rendered accordingly.
The second part is maing all changes to the client side scroll positions known to the server side code, and that's where theimplementation is missing... the framework lacks support for firing those events to the serverside code.
Hope this explains,