Considering they mentioned OSX and Linux, of which IE is available on neither (Safari is default on OSX, and Linux is distro specific, usually Firefox, Konqueror or Epiphany) I don't think IE is necessarily the big issue, but the issue that many people maybe using many different browsers.
I myself run Arch Linux, and I primarily use Chrome, I have Epiphany installed (came with gnome-extras), along with Minefield x64 (Firefox) which I occasionally use when something doesn't work on Chrome (ironic, I know). Just picking something to stick too can make a lot of processes between users and co-workers easier.