I don't know if this is a concern, but is SilverStripe supported on IE6?
I have a client who keeps using it (although I'm trying to wean her on to Firefox) and she found an interesting bug. In Files & Images, select any file and take a look at the View/Edit Asset window. The Save button is totally missing (!) and the window misbehaves itself quite mischievously whenever you click on a tab or click into one of the form input fields.
As I say, maybe you don't support IE6 (I personally wouldn't either) but I thought I'd mention it.
That widget is no indication about IE 6 compatibility. It's just there for people who don't make their site work in IE6 and want to display a warning to the user.
But as far as I know it's true that the SilverStripe CMS doesn't work well (or at all) in IE6. It's important to differentiate between the SilverStripe CMS and the SilverStripe driven Website or Application, since it's up to you (the developer) to make that work in IE 6 or not...