So if there are ways to make pages accessible to older systems, that is a very good thing. Of course, I'll never be able to use it, but someone else probably can.
Just because something exists(or can be called "legacy") doesn't mean it should be supported. I would venture to guess that nobody in the world uses any of the browsers shown on any regular basis. And if they do, they have absolutely no expectations of it working correctly.
When IE 1.5 was launched 8MB of RAM was acceptable and people were excited about 28.8k modems.
It depends on where they work. We have to support IE6/7 because our users are largely accessing the webapp from hospitals... which means they're using computers that are very strictly controlled by the IT department, because upgrades can break other, very expensive legacy software that relies on old IE versions or other particular quirks of old OS versions. And if you break some essential medical software, lives can be at stake, so they can't take it lightly.
To be sure, they don't assume that our webapp will work in the browsers they're forced to use. But if it doesn't, we can't possibly get them as a customer until some distant day when they are ready to lay out the serious investment required to upgrade.