> Chrome / FF now have a combined 700 million and I'd assume between 50 - 70% of the browser marketshare
They have 55% and IE has 35%, but it's much worse than that in a lot of English-speaking countries (like the USA, where IE has 43%). Additionally, older (read: richer) demographics are more likely to use IE than average. So are workplaces (read: corporate customers). IE support being mandatory isn't an "assumption" it's basically a fact. If you're writing for the public web, you probably have to support IE8, and if you're selling things or have corporate customers, it gets even more important.
They have 55% and IE has 35%, but it's much worse than that in a lot of English-speaking countries (like the USA, where IE has 43%). Additionally, older (read: richer) demographics are more likely to use IE than average. So are workplaces (read: corporate customers). IE support being mandatory isn't an "assumption" it's basically a fact. If you're writing for the public web, you probably have to support IE8, and if you're selling things or have corporate customers, it gets even more important.
http://gs.statcounter.com/#browser-ww-monthly-201110-201210-...