Well I discussed this at work.
Why do people still use the fugly IE 5.5?
Answer: Because its installed by default. Upgrades to a newer browser are optional, and alot of people dont run updates at all.
The later update packs/windwos give you a choice of a other default browser, because some lawsuit about monopoly position. But people still choose IE, because they think IE is the internet! And you think thats only a few old ladies, but ALOT of people think that IE is the internet.
See this questionary:
http://www.youtube.com/watch?v=o4MwTvtyrUQ
My point is, people are either going WOW this is bad, I miss my old content and install google chrome/mozilla and we are shed of the tug IE has cast on so many front end developers with its incompatibilty and weird hacks. OR more likely, people will use the default browser like they always did, in this case the default metro browser without plugins and flash.
It has happen before, when microsoft released I think IE 6 where they just disabled Javascript and ActiveX components per default, because at that time, lots of adds were installing toolbars in IE because of security leaks. People still use that browser, and it took years before it got fixed.