For all web developers and designers, Internet Explorer 8 support is likely the least enjoyable part of your work, and it's unlikely to go away any time soon. As much as Microsoft would like for everyone to upgrade to Windows 8 this fall, the simple truth is that many home and school PCs are still running Windows XP. These systems are for the most part under powered to run Windows 7, and may have software that is incompatible with the newer versions of Windows. After all, from XP there is Vista, 7, and very soon, Windows 8. Just think about all the driver incompatibilities introduced by each successive operating system upgrade.
For large organizations, such as academic institutions, an en masse upgrade from XP is unlikely, not only for the hardware and licensing costs, but also through the IT management work required to vet any software upgrades. The upgrades happen, albeit slowly. There just isn't a compelling enough reason to upgrade.
Why doesn't Microsoft just upgrade the version of Internet Explorer running on XP? Why can't they put IE 9, and soon IE 10, on their older operating system? The latest versions of Mozilla Firefox, Google Chrome, and Apple's Safari are all available for Windows XP.
But all those browsers are cross-platform, one might argue. They don't have the deep integration with the operating system, like IE has. So what? Why should that matter? Safari is a web browser installed by default with Mac OS X, which presumably has as much opportunity for deep OS integration as IE. Apple took a different route. Rather than seeking deep integration with the OS, Apple open sourced the WebKit rendering engine, which is now not only used by Google Chrome, but also in most smartphone browsers as well, including those of BlackBerry, Android, and iOS.
One could argue that this kind of entrenchment, where Microsoft is unwilling or unable to upgrade the browser in earlier versions of Windows, is exactly the kind of problems the Department of Justice antitrust case should have solved. Certainly, the arguments raised by Microsoft suggested that the operating system was strongly coupled with the web browser, such that they could not be separated. But the antitrust trial focused on competitor access to Microsoft APIs. If the sanctions against Microsoft had been stronger, we might have seen IE9 on Windows XP today.
Microsoft is clearly capable of writing a rendering engine separate from the OS. From 1998 to 2003, Microsoft released versions of Internet Explorer for the Mac, dropping support in December of 2005. These versions were supported on Mac OS 7, the "Classic" OS, through to OS X Tiger, and supported two different system architectures, the old Motorola 68k systems, as well as the PPC systems. They have experience in writing cross-platform rendering engines, but clearly feel hat one closely tied to a particular operating system version is somehow beneficial.
How exactly does a tightly coupled system help them? It could be an added enticement to upgrade to a newer version of Windows, but if so, it's not really very effective. Perhaps it makes development easier? I fail to see how that might be the case. Other browsers seem to have no problems with a more portable architecture, so unless Microsoft is making extensive use of internal APIs again (once again, reference the antitrust suit),I fail to see how this makes sense.
One of the most convincing arguments is that it could cut the number of possible OS/browser configurations for testing, either internally, or by organizations with more extensive upgrade trials. Supporting IE9 on Windows XP would need extensive testing not inly of the browser itself, but all the different extensions and integrations, all on an operating system that is several generations old. After all, XP is in extended support mode, with that final stage set to expire in April 2014. Spending large amounts of money on testing IE9 support on Windows XP clearly isn't in Microsoft's best interests.
So where does that leave web developers today? Are we doomed to support IE until 2014? Sadly, I suspect it will live on longer, the browser zombie of the net. Aside from promoting the use of Firefox or Chrome on Windows XP, there is little we can do. Like classic Romero zombies, it's not going anywhere very fast.