If IE6 were holding it back for so long, why did it miraculously stop, even though nothing changed? The answer, of course, is that it wasn't IE6. It was the lack of a business model, which was inadvertently solved by Google.
Saying IE6 held the browser market back is like saying Yahoo held the search market back by giving it away for free. Just like Yahoo, Microsoft is now feeling the pain of failure to innovate.
Of course, everyone here hates IE6 (understandably) and Microsoft so I'll get downmodded a lot.