Why did IE9 leave out support for the File API and the multiple attribute on file inputs?

Why did IE9 leave out support for the File API开发者_StackOverflow中文版 and the multiple attribute on file inputs? Chrome, Firefox and Safari support the features. But IE9 (and Opera) failed to support these for some unknown reason. For IE9 it seems we're still stuck with Flash for multiple file upload support (iframe hacks do not count).

File API is still a 'Working Draft'.

Internet Explorer 10 will support File API (prototype) More Details