Agreed, but I can't shake the feeling this is a self-fulfilling prophecy.
You're advising to act like they'll still be the dominant player in a few years, but by supporting them this way it's indeed true that this will be the case. See the vicious circle?
However you look at it they are the largest player, and you have to design for it. Having a website that doesn't work in IE is like having a store where you have a guy at the door telling 4 out of five people that they can't come inside to buy your stuff.
I don't particularly like MS, and I don't agree with their tactics but that doesn't mean I make the naive mistake of dismissing them or thinking that in a few years they'll be gone. They won't, so be a little pragmatic.
IE is in no way irrelevant, nor is it becoming so in the near future.