you say "... installing a VM in Virtualbox (free) is straightforward."  It isn't very straightforward.  Also while Virtualbox may be free, Microsoft Windows (to you know, install on your VM) isn't.  Ignoring the very real option of stealing Microsoft Windows, it should be noted that buying an operating system (and to really make certain your test environment matches your user base you probably need both XP and 7 so it's more like two OSes on two VMs, still sound straightforward?) from a company that is already making your life difficult by having distributed the hideously non-compliant IE6-8 to the masses just isn't terribly appealing.  Of the five major browsers, (Firefox, Opera, Safari, Chrome, IE) all of them are available for all major OSes except one.  If Microsoft wants web developers to support their browser they ought to make it available for the OS that comes with web developer's MacBooks.  The point remains that Paydirt is doing a good thing by pushing users towards modern browsers and Microsoft needs to give up and start distributing Windows with Chrome or Firefox (I'm assuming Safari would be way too much of a political concession).