I have a few things I\'ve made in the past that have the border-radius attribute like this:
border-radius: 7px;
This is not working in IE9. I t
IE9 does support border radius, even shorthand. I'm not sure why it doesn't work on your website, but it is supported.
(See http://jsfiddle.net/wJd2h/ for proof)
IE9 also supports :last-child.
Maybe you are using an old HTML doctype?
EDIT: I looked at your source. Change to