OK.
See where it says "http://www.microsoft.com" in the URL bar? And yet, the browser is on Secunia's web site.
Suppose I am an Evil Nigerian, and I send you one of those fake emails that says you should Watch Out for the Novarg virus, and you should update Windows right now by clicking here.
You click, and sure enough, you go to a Microsoft page. It even says "http://www.microsoft.com" in the URL bar. And it's asking for your Passport ID and password.
But it isn't a Microsoft page. It's really www.evilnigerians.com.
You're so smart that you wouldn't be fooled by that, but there are probably 6x1023 people who would be fooled by that. And the Evil Nigerians would have their Passport ID's. Or their credit card number... these scammers are pretty clever. All they have to do is gin up a halfway-decent knockoff of a reputable web site, and then send out a millions spams tricking people into coming to disney.com or whatever to buy a stuffed Mickey Mouse for $1.50. Next thing you know, the Evil Nigerians will have 100,000 credit card numbers complete with name, address, and phone number.
As you know, there is an official Microsoft talking point on this feature. It is that this is not a flaw in a Microsoft product, because it doesn't do anything. And if it does do something, it is still not a flaw in a Microsoft product... it is stupid people being stupid. And if it is a flaw, it isn't Microsoft's fault; it's godless linux communists and their foreign precious bodily fluids. And if you try to defend yourself from this seemingly endless series of security holes in this totally flawless product by getting and using something else, then you personally are a godless communist and you probably rip off the music companies too and you pray to Richard Stallman and your father marched with Hitler.
In spite of which, game theory tells us that there is an advantage to be gained by being among the first to get and use something else. It is probably true that if Firebird (or whatever) someday achieves the 80% market share that IE has now, the Evil Nigerians will target Firebird. But right now they don't, and they probably won't for a few years at least. So there will be a few years of peace and quiet for those who got in on the Firebird trend first.