On the face of it, the delay is a little surprising. Internet Explorer 10 is included with Windows 8, and since Windows 8 was completed back in August, clearly Internet Explorer 10 must in some sense be finished. The extra time required for Windows 7 may be due to underlying platform differences—Windows 8 supports Direct3D 11.1, compared to 11.0 on Windows 7, for example. So if Internet Explorer 10 depends on Direct3D 11.1 features, either that dependence has to be removed, or Direct3D 11.1 has to be ported to Windows 7.
This would not be unprecedented. Internet Explorer 9 depended on features such as Direct2D and DirectWrite that were built in to Windows 7. To enable the browser to run on Windows Vista, Microsoft shipped an update package that added the new capabilities to the older operating system.
The November preview will be the first version of Internet Explorer 10 to run on Windows 7 since Platform Preview 2 back in June of last year. Subsequent releases were restricted to Windows 8 only. Rather than shipping standalone previews of the browser engine, Microsoft used the Windows 8 Developer, Consumer, and Release Previews to serve double duty as Internet Explorer previews.
Unlike those two Platform Previews—which embedded the new rendering engine into a rudimentary container that lacked even a back button—the November release will be a full browser preview. It will include not just a rendering engine, but also a full browser user interface and shell.
