Although it's clear that the Internet Explorer team has done a very good job optimizing their software for that dusty old Tegra SoC, there are two reasons why IE on Surface might seem more performant than rival tablets:
1. It's rendering 1/4 of the pixels of a Nexus 10 or iPad 4. Of course pages will tend to render and scroll faster, since it's actually doing less work. Some pages will actually load higher-quality assets to high resolution displays, so they also take more time to transfer over the network as well as to render.
2. Microsoft knows that there won't be an RT device with less than 2GB of RAM out there, while other browsers need to be able to run on devices with as little as 256MB of RAM. So for example, IE can afford to load in all images on a page, while Safari and Chrome are designed to stream those assets as the user requests them in order to conserve memory.
"The worst part about these reviews is they are [subjective]--and their scores often depend on how drunk you got the media at a Street Fighter event." — Mona Hamilton, Capcom Senior VP of Marketing
*Image indefinitely borrowed from BrainBoxLtd without his consent.
