Microsoft has promised to improve touchpad support in Windows 8.1, but some users are actually reporting problems with scrolling in the Preview version.
According to several posts on Microsoft's support forums, scrolling doesn't seem to work on specific computers after deploying Windows 8.1 Preview.
It appears that it's a problem caused by incompatible drivers, so users are recommended to wait for the final build or until the manufacturer releases a new set of drivers for their touchpads that could work on Windows 8.1.
“Since Windows 8.1 is still in a preview phase, many device manufacturers have not yet released drivers for their device. You may however, contact the manufacturer and keep them informed about it so that they may work on an updated driver for the touchpad,” a Microsoft support engineer explained.