Microsoft obviously knows that the only way to kill IE6 is to say it is unsupported software and to stop releasing security updates for it. Until that happens, IT departments will continue to cling to it as part of the default install of Windows XP.
This is the same approach which will be necessary to address endemic security and reliability failures caused by bad architectural choices made for single-user desktops in the 90s. Since they finally shipped MED-V I suspect they'll probably use that approach and tell corporate customers that the only way to continue running IE6 is in an XP VM with some sort of on-demand launch scheme.
1. Setting an HTTP header would be easier but seems likely to allow phishers to opt-in to security holes and there's an argument that pushing the support cost off to app owners is better any way.