In IE10 the JavaScript is multithreaded... there's a separate thread for JS parsing, compiling, and garbage collection. As far as I know this is the only browser with a threaded JavaScript VM. So the skipping frames is probably because the rendering can be done independently from running JavaScript, and the core in use is probably some quirk like the benchmark creating a few objects on a timer, causing the GC to run on another thread -- that kind of thing can be fixed pretty easily, either by tweaking the benchmark (if it were publicly available) or by Microsoft fixing IE.

I haven't actually used IE10 yet, but I think you'll find this new architecture makes overall browsing more responsive and smoother than Chrome.