When the upcoming Drupal 8 arrives, it will be without the ie7.css file that provides compatibility support.
The decision was based on the falling usage percentage of the browser, which should find a new low once Microsoft completes its IE6 and IE7 automatic-upgrade process.
Deprecating IE7 will allow Drupal 8 to take advantage of IE8’s additional features and faster JavaScript execution compared to IE7 — CSS-generated content, full display property support, and proper JSON parsing.
Drupal 8 is expected to be released during 2013 or 2014.
The CMS is far from alone in dropping IE7 support; Facebook prevents IE7 users from viewing its Timeline feature, Google Apps has ended support for IE7, and jQuery is considering ending mainline support for IE6, IE7, and IE8 in the upcoming jQuery 2.0 release.
