Governments (UK, Argentina, most LA) validating IE as their default browser (i mean, not a bylaw but the whole country) since IE6 and never upgraded for almost a decade? and, Windows XP is by far the most installed OS in the world, with ie6 sp1 as the primary browser.
ie6 will be here until 2014 for final users and for goverments, i would add 5 more (at least in LA).
will the world be here by then? who knows, make your work the easier you can. at any cost.
would your client plus$$ you for your ie6 version? mmm.
on the other hand, would you induce losses to a client because the visitors navigate the www with an obsolete software and you don't "support ie6 anymore"?
its an cyber-educational thing, people will realise one day (maybe prior 2014) that a browser is not a folder.