There could be somewhat of a chicken-and-egg thing happening here with their low IE take-up. On IE 9 the slideshow on the home-page doesn't work, it just says "... loading fancy-pants slideshow ...". If I came across that as an IE user, I wouldn't be signing up.
There is also the demographic for their product, which is the more-likely reason for low IE rates. I wouldn't be surprised if the big Mac-OS screen shot on the home page turns off Windows users as well.
There is also the demographic for their product, which is the more-likely reason for low IE rates. I wouldn't be surprised if the big Mac-OS screen shot on the home page turns off Windows users as well.