I scroll all the time. So it should better work perfectly. With Chrome, it doesn't. Switching between my feedreader and Chrome made my fingers hurt.
(This is, by the way, something many OS X apps get wrong. All of MS Office, iTunes and so on.)
If they did, Safari on Windows would look and feel more like a Windows application. As it stands, it's a very opinionated application, with foreign-looking scrollbars, text antialiasing that works differently from ClearType (they may have changed this by now, I haven't looked), etc. Comparing market shares between these browsers with the assumption that they have the same goals might be a bit off.
[edit]: I've also noticed a lot of people I know living over in the Windows world seem to harbor an uncontrolled hate-on for iTunes and Quicktime. Since these are often associated with the installation of Safari, that probably doesn't help Apple's position. Does Chrome come with any "unwanted" extras?
It's because Apple's software runs like garbage on Windows boxes. They eat up resources, install unnecessary stuff, run useless background apps that east up memory, take over bindings between file types and better applications (really, quicktime? I really don't want you to become the embedded player for .mpg files in all of my browsers, so I'm stuck with a 1"x1" postage stamp on my 26" monitor and no full-screen option).
On Macs, the software is sublime. On PCs they simply suck.
Those specific pieces of software alone kept me away from Macs for years because the PC ports were so terrible.
Plus Safari is very close to Chrome's performance on a Mac, at least insomuch that anyone wouldn't notice.
That being said, although Chrome performs the core browser functions better than safari, it's still rough around the edges.
Really, there isn't any meaningful debate that V8 is the current king of the hill in Javascript performance, by a pretty large margin. Your statement that Safari's engine runs faster than Chrome's isn't supported by any evidence of which I am aware.
source: http://www.computerworld.com/s/article/9142004/Safari_edges_...
Now of course on Windows there is no contest, Chrome is faster, but on Mac Safari is slightly faster.