I see your point and I would think they would work hard to at least make their main page work for people using IE, but everyone else also has valid points.
You would code for your target audience and then try to make it work with the other browsers. I am primarily a Linux user (except when I am at work unfortunately) so if I were to make anything it would be coded for Firefox, and if I had the time and found the problems dumb it down so it works in IE.
Also for my Linux based blog and website, I am using a CMS so it works across the board but if a part didn't work in IE I really wouldn't care. Most of the target audience won't/can't use IE so why does it matter to me.
Still, it would be a poor business decision to not allow IE for a company that is trying to market an online service like that, but hey, its their bottom line.