SmartNavigation only works for the most trivial website. When you do anything custom (anything besides drag-n-drop development), smartnavigation breaks your page, and it won’t even post back. This scroll problem is an issue for ASP.NET since the postback method is widely used.
I have run across some older user will bad eyesight, and they are at 800×600 resolution, so they do A LOT of scrolling both vertically and horizontally. Retaining scroll position will mean a better user experience for them.