"Microsoft can release this for Windows 7 and still hinder development of web apps."
So, instead of building a better browsing experience, they should port IE9 back to XP... despite it not supporting half of what they need it to support to do what IE9 is doing?
I understand what you are asking. I understand why you think it's reasonable. I disagree, however, because it's not reasonable, and it's a very bad idea for many reasons. It's also silly, and ignorant.
Edit: Ignorant might sound strong, but I really do think you just don't know why backporting IE9 to XP is probably a bad idea. I'm not calling you stupid.
The only bad reason that I can think of is that they might want to use IE9 as an incentive for XP users to upgrade to Win7. I can't think of any others. (Maybe you could share.)
If XP users want a more compliant browser without upgrading from XP, they'll have no problem, though, so this doesn't sound like a good choice of leverage on Microsoft's part.
It's quite simple. IE9 will be making use of OS features that aren't available on XP, which is after all a nine year old OS. MS have chosen to take advantage of OS features in their OS-specific browser. No mystery.
I was kind of hoping for something more specific. After all, WebKit manages to use modern APIs (CoreAnimation, etc.) on MacOS X, yet Chrome and Safari both ship on XP. Can you think of anything that can't be easily shimmed?
There is a reason Safari on OSX performs much better then on Windows. Safari and Chrome are differnet browsers. Safari on Mac is different from Windows, even at the basic level. Web Kit is a foundation, not the end result.
Run over to the IE9 testing site, and run the animated stuff on Chrome and on Safari, and you'll see abysmal results when run on a Windows machine. Then, run the same test with Safari on Mac, and it will be like night and day.
Now, if IE9XP can't support the same features of IE9Win7 like SafWin can't support the same features as SafOSX, then there is arguably more harm in supporting XP from a developer stand point, and therefore, a user standpoint. As a developer, it's like having 2 more browsers to check for IE9XP/IE9Win7.
That's not even getting into the security concerns with XP.
I'll hazard a guess that this might have to do with the success they've had in getting users to update off of old versions. While you might be able to find a Tiger box out in the wild, I bet you'd never find someone running Cheetah. Doesn't over 60% of HTTP traffic come from XP boxes, in contrast?
They are using Direct2D (or DirectSomethingOrOther) for the hardware accelerated rendering. I don't believe this is available on XP. There will no doubt be a bunch of other Win7/Vista specific bits of functionality that would build up to an appreciable amount of hassle when implementing an XP version.
Yeah, I know. So what?
"Microsoft can release this for Windows 7 and still hinder development of web apps."
So, instead of building a better browsing experience, they should port IE9 back to XP... despite it not supporting half of what they need it to support to do what IE9 is doing?
I understand what you are asking. I understand why you think it's reasonable. I disagree, however, because it's not reasonable, and it's a very bad idea for many reasons. It's also silly, and ignorant.
Edit: Ignorant might sound strong, but I really do think you just don't know why backporting IE9 to XP is probably a bad idea. I'm not calling you stupid.